:  h  iV; 


II.   Secondary  Age. 

I    Palaeozoic  Age. 
Metamorphic  Rocks. 

G&F  TH1 


Upper  Tertiary  Formation 

Lower  Tertiary  " 
Cretaceous 

Oolitic  " 

Trias  " 

Carboniferous  " 

Devonian  " 

Upper  Silurian  " 

Lower  Silurian  " 


PRINCIPLES  OF  ZOOLOGY: 

TOUCHING 

THE    STRUCTURE,    DEVELOPMENT,    DISTRIBUTION, 
AND    NATURAL    ARRANGEMENT 


RACES  OF  ANIMALS,  LIVING  AND  EXTINCT 

WITH  NUMEROUS  ILLUSTRATIONS. 
PART  I 

COMPARATIVE    PHYSIOLOGY. 

FOR  THE  USE  OF  SCHOOLS  AND  COLLEGES. 
BY 

LOUIS    AGASS1Z  AND  A.  A.  GOULD, 

REVISED      EDITION. 


BOSTON: 
OOULD     AND      LINCOLN, 

50     WASHINGTON    STREET. 

NEW    YOKK:     SHELDON    AND    COMPANY. 
CINCINNATI :  GEO.  S.  BLANCUAKD. 

1869. 


Entered,  according  to  Act  of  Congress,  in  the  year  1851 

BY  GOULD  AND  LINCOLN, 
In  the  Clerk's  Office  of  the  District  t'oort  tor  the  District  of  Massachusetts. 


PREFACE. 


THE  design  of  this  work  is  to  furnish,  an  epitome  of  the  leading 
principles  of  the  science  of  Zoology,  as  deduced  from  the  present 
state  of  knowledge,  so  illustrated  as  to  be  intelligible  to  the  begin- 
ner. No  similar  treatise  now  exists  in  this  country,  and,  indeed, 
some  of  the  topics  have  not  been  touched  upon  in  the  English  lan- 
guage, unless  in  a  strictly  technical  form,  and  in  scattered  articles. 
On  this  account,  some  of  the  chapters,  like  those  on  Embryology 
and  Metamorphosis,  may,  at  first,  seem  too  abstruse  for  scholars  in 
our  common  schools.  This  may  be  the  case,  until  teachers  shall  have 
made  themselves  somewhat  familiar  with  subjects  comparatively  new 
to  them.  But  so  essential  have  these  subjects  now  become  to  a  correct 
interpretation  of  philosophical  zoology,  that  the  study  of  them  will 
hereafter  be  indispensable.  They  furnish  a  key  to  many  phenomena 
which  have  been  heretofore  locked  in  mystery. 

Being  intended  for  American  students,  the  illustrations  have  been 
drawn,  as  far  as  possible,  from  American  objects  :  some  of  them  are 
presented  merely  as  ideal  outlines,  which  convey  a  more  definite 
idea  than  accurate  sketches  from  nature  ;  others  have  been  left  im- 
perfect, except  as  to  the  parts  especially  in  question  ;  a  large  propor- 
tion of  them,  however,  are  accurate  portraits  from  original  drawings. 
Popular  names  have  been  employed  as  far  as  possible,  and  to  the 
scientific  names  an  English  termination  has  generally  been  given ; 
but  the  technical  terms  have  been  added,  in  brackets,  whenever  mis- 
understanding was  apprehended.  Definitions  of  those  least  likely 
to  be  understood,  may  be  found  in  the  Index. 

The  principles  of  Zoology  developed  by  Professor  Agassis  in  his 
published  works  have  been  generally  adopted  in  this,  and  the  results 
•)f  many  new  researches  have  been  added. 

The  authors  gratefully  acknowledge  the  aid  they  have  received, 
in  preparing  the  illustrations  and  working  out  the  details,  from  Mr. 


6  PREFACE. 

E.  Desor  for  many  years  an  associate  of  Professor  Agassiz,  from  Count 
Pourtales  and  E.  C.  Cabot,  Esq.,  and  also  from  Professor  Asa  Gray, 
by  valuable  suggestions  in  the  revision  of  the  letter-press. 

The  first  part  is  devoted  to  Comparative  Anatomy,  Physiology, 
and  Embryology,  as  the  basis  of  Classification,  and  also  to  the  illus- 
tration of  the  geographical  distribution  and  the  geological  succession 
of  Animals ;  the  second  to  Systematic  Zoology,  in  which  the  prin- 
ciples of  Classification  will  be  applied,  and  the  principal  groups  of 
animals  will  be  briefly  characterized. 

Should  our  aim  be  attained,  this  work  will  produce  more  enlarged 
ideas  of  man's  relations  to  Nature,  and  more  exalted  conceptions  of 
the  Plan  of  Creation  and  its  Great  Author. 

BOSTON,  June  1,  1848. 


PREFACE   TO  THE   REVISED   EDITION. 

IN  revising  the  present  work,  the  authors  have  endeavored  to 
render  more  precise  those  passages  which  admitted  of  too  broad  a 
signification  or  of  a  double  interpretation;  and  to  correct  such  errors 
as  had  arisen  from  inadvertence,  or  such  as  the  rapid  progress  of  Sci- 
ence has  disclosed.  They  are  indebted  for  many  suggestions  on 
these  points  to  several  distinguished  teachers  who  have  used  the  work 
as  a  text  book,  and  more  especially  to  Professor  Wyman,  of  Harvard 
University.  Several  entirely  new  paragraphs  have  also  been  added. 

A  list  of  some  of  the  principal  authors  who  have  made  original 
researches,  or  of  treatises  which  enter  more  into  detail  than  was  ad- 
missible in  an  elementary  work,  has  been  given  at  the  close  of  the 
volume*  for  the  use  of  those  who  would  pursue  the  subject  of 
Zoology  in  a  more  extended  manner. 

The  work  having  thus  been  revised  and  enlarged,  the  authors  sub- 
mit it  to  the  public  with  increased  confidence  in  its  accuracy  and 
usefulness. 

BOSTON,  February  1,  1851. 


TABLE  OF  CONTENTS. 


Page 

INTRODUCTION     ....  ...        17 


CHAPTER  FIRST. 

THE  SPHERE  AND  FUNDAMENTAL  PRINCIPLES  OP  ZOOLOGY    .  '-5 

CHAPTER   SECOND. 
GENERAL  PROPERTIES  OF  ORGANIZED  BODIES      .       .       ,  35 

SECTION  I. 
Organized  and  Unorganized  Bodies         .......  85 

SECTION  II. 
Elementary  Structure  of  Organized  Bodies         ....  36 

SECTION  III. 
Differences  between  Animals  and  Plants         .        .  •        •  41 

CHAPTER  THIRD. 

FUNCTIONS  AND  ORGANS  OF  ANIMAL  LIFE          .  44 

SECTION  I. 
0]  the  Nervous  System  and  General  Sensation      .  .  M 


TABLE    OF    CONTENTS. 

SECTION  II.  p^ 

Of  the  Special  Senses    .  .48 

1.  Of  Sight        .                 48 

2.  Of  Hearing ...  65 

3.  Of  Smell 60 

4.  Of  Taste                   . 62 

5.  OfTouch      .                63 

6.  Of  the  Voice    .  34 


CHAPTER  FOURTH. 

OF  INTELLIGENCE  AND  INSTINCT                .  67 

CHAPTER   FIFTH. 

OP  MOTION ...  73 

SECTION  I. 

Apparatus  of  Motion ...  73 

SECTION  II. 

Of  Locomotion 7^ 

1.  Plan  ol  the  Organs  of  Locomotion       .  82 

2.  Of  Standing,  and  the  Modes  of  Progression           ...  88 

Walking 90 

llunning          . 91 

Leaping 91 

Climbing 92 

Flying 92 

Swimming ...  93 

• 

CHAPTER  SIXTH. 

OP  NUTRITION 96 

SECTION  I. 

Of  Digestion 9? 

Digestive  Tube          ....                ....  9? 

Chymification 100 

Chylification 100 

Mastication            ...                .                ....  101 

Insalivation        .......                .  108 

Deglutition    ...                                .                ...  108 


TABLE    OF    CONTENTS. 

CHAPTER   SEVENTH. 
OP  THE  BLOOD  AND  CIRCULATION         ....  .111 

CHAPTER   EIGHTH. 
OF  RESPIRATION  118 

CHAPTER  NINTH. 
OF  THE  SECRETIONS 126 

CHAPTER  TENTH. 
EMBRYOLOGY 1^J 


SECTION  I. 

Of  the  Egg 131 

Form  of  the  Egg 

Formation  of  the  Egg 1^ 

Ovulation 

Laying • 

Composition  of  the  Egg          .  ...  137 

SECTION  II. 
Development  of  the  Young  within  the  Egg 138 

SECTION  III. 
Zoological  Importance  of  Embryology    .......  V>3 

CHAPTER   ELEVENTH. 
PECULIAR  MODES  OF  REPRODUCTION     .  156 

SECTION  I. 
Qemmiparous  and  Fissiparous  Reproduction         ...  156 

SECTION  II. 
Alternate  and  Eqidvocal  Reproduction  158 


10  TABLE  OF  CONTENTS. 

SECTION  III. 

Fagk 

Consequences  of  Alternate  Generation       ....  ,16? 

CHAPTER  TWELFTH. 

METAMORPHOSES  OF  ANIMALS    .....  174 

CHAPTER  THIRTEENTH. 

GEOGRAPHICAL  DISTRIBUTION  OF  ANIMALS        .  i8G 

SECTION  I. 
General  Laios  of  Distribution        ....  ,  l&G 

SECTION  II. 

Distribution  of  the  Faunas        .....  194 

I.  Arctic  Fauna       ......        ..  197 

II.  Temperate  Faunas        .....  198 

III.  Tropical  Faunas      .....        .  204 

SECTION  III. 
Occlusions        .......  ...  207 

CHAPTER   FOURTEl'A'rH. 


GEOLOGICAL  SUCCESSION  OF  ANIMALS;  OB,  Tpaa 

IN  TIME       ..........  '214 

SECTION  I. 

Structure  of  'he  Earth's  Crust  ...'....  214 

SECTION  II. 

Ages  of  Nature        ..........  221 

Palaeozoic  Age      ..........  223 

Secondary  Age        .        ........  227 

Tertiary  Age       ..........  233 

Modern  Age  ....  ....  235 

Conclusions        .        .        ;  ?3? 


EXPLANATION    OF    THE    FIGURES. 


FRONTISPIECE.  —  The  diagram  opposite  the  title  page  is  intended  to 
present,  at  one  view,  the  distribution  of  the  principal  types  of  animals, 
and  the  order  of  their  successive  appearance  in  the  layers  of  the  earth's 
crust.  The  four  Ages  of  Nature,  mentioned  at  page  221,  are  represented 
by  four  zones,  of  different  shades,  each  of  which  is  subdivided  by  circles 
indicating  the  number  of  formations  of  which  they  are  composed.  The 
whole  disk  is  divided  by  radiating  lines  into  four  segments,  to  include  the 
four  great  departments  of  the  Animal  Kingdom ;  the  Vertebrates,  with 
Man  at  their  head,  are  placed  in  the  upper  compartment,  the  Articulates 
at  the  left,  the  Mollusks  at  the  right,  and  the  Radiates  below,  as  being 
the  lowest  in  rank.  Each  of  these  compartments  is  &gain  subdivided  tc 
include  the  different  classes  belonging  to  it,  which  are  named  at  the  outer 
circle.  At  the  centre  is  placed  a  figure  to  represent  the  primitive  egg, 
with  its  germinative  vesicle  and  germinative  dot,  (278,)  indicative  of  the 
universal  origin  of  all  animals,  and  the  epoch  of  life  when  all  are  appar- 
ently alike,  (275,  276.)  Surrounding  this,  at  the 'point  from  which  each 
department  radiates,  are  placed  the  symbols  of  the  several  departments, 
as  explained  on  page  155.  The  zones  are  traversed  by  rays  which  repre- 
sent the  principal  types  of  animals,  and  their  origin  and  termination  in- 
dicates the  age  at  which  they  first  appeared  or  disappeared,  all  those  which 
reach  the  circumference  being  still  in  existence.  The  width  of  the  ray  in- 
dicates the  greater  or  less  prevalence  of  the  type  at  different  geological 
ages.  Thus,  in  the  class  of  Crustaceans,  the  Trilobites  appear  to  com- 
mence in  the  earliest  strata,  and  to  disappear  with  the  carboniferous  for- 
mation. The  Ammonites  also  appeared  in  the  Silurian  formation,  and 
did  not  become  extinct  before  the  deposition  of  the  Cretaceous  rocks. 
The  Belemnites  appear  in  the  lower  Oolitic  beds  ;  many  forms  commence 
in  the  Tertiary ;  a  great  number  of  types  make  their  appearance  only  in 
the  Modern  age ;  while  only  a  few  have  continued  from  the  Silurian, 
through  every  period  to  the  present.  Thus,  the  Crinoids  were  very  nu- 
merous in  the  Primary  Age,  and  are  but  slightly  developed  in  the  Tertiary 
and  Modern  Age.  It  is  seen,  at  a  glance,  that  the  Animal  Kingdom  is 
much  more  diversified  in  the  later  than  in  the  earlier  Ages. 

Below  the  circle  is  a  section,  intended  to  show  more  distinctly  the  rel- 
ative position  of  the  ten  principal  formations  of  stratified  rocks  (461) 
composing  the  four  great  geological  ages ;  the  numerals  corresponding  to 
those  on  the  ray  leading  to  Man,  in  '.he  circular  figure.  See  also  figure  154. 


12  EXPLANATION    OF    THE    FIGURES. 

THE  CHART  OF  ZOOLOGICAL  REGIONS,  page  195,  is  intended  to  show 
the  limits  of  the  several  Faunas  of  the  American  Continent,  correspond- 
ing to  the  chmatal  regions.  And  as  the  higher  regions  of  the  mountains 
correspond  in  temperature  to  the  climate  of  higher  latitudes,  it  will  be 
seen  that  the  northern  temperate  fauna  extends,  along  the  mountains  of 
Mexico  and  Central  America,  much  farther  towards  the  Equator  than  it 
does  on  the  lower  levels.  In  the  same  manner,  the  southern  warm  fauna 
extends  northward,  along  the  Andes. 

FlQ. 

1.  Simple  cell,  magnified,  as  seen  in  the  house-leek. 

2.  Cells  when  altered  by  pressure  upon  each  other ;  from  the  pith  of  elder. 

3.  Nucleated  cells,  (a,)  magnified;  b,  nucleolated  cells. 

4.  Cartilaginous  tissue  from  a  horse,  magnified  120  diameters. 

5.  Osseous  tissue  from  a  horse,  magnified  450  diameters. 

6.  Nervous  fibres,  showing  the  loops  as  they  terminate  in  the  skin  of  a 

frog. 

7.  Gray  substance  of  the  brain,  magnified. 

8.  Head  of  an  embryo  fish,  to  show  its  cellular  structure  throughout 

9.  Diagram,  to'show  the  nervous  system  of  the  Vertebrates,  as  found 

in  a  monkey. 

10.  Diagram  of  the  nervous  system  of  the  Articulates,  as  seen  in  a  lobster. 

11.  Diagram  of  the  nervous  system  of  the  Mollusks,  as  found  in  Natica 

heros. 

12.  Diagram  of  the  nervous  system  of  the  Radiates,  as  found  in  Scutella, 

( Echinarachnius  parma. ) 

13.  Section  of  the  eye.    a,  optic  nerve ;  b,  sclerotic  coat ;  c,  choroid  coat; 

d,  retina ;  e,  crystalline  lens  ;  /,  cornea ;  gt  iris  ;  A,  vitreous  body ; 
iy  chamber,  divided  by  the  iris. 

14.  Diagram,  showing  the  effect  of  the  eye  on  rays  of  light. 

15.  Position  of  the  eye  of  the  snail. 

16.  Eyes  (ocelli)  of  the  spider. 

17.  Eye-spots  of  a  star-fish,  (Echinaster  sanguinolentus.) 

18.  Compound  eyes,  showing  the  arrangement  of  the  faoettes,  and  theii 

connection  with  the  optic  nerve,  as  seen  in  a  crab's  eye. 

19.  Diagram  of  the  human  ear,  to  show  the  different  chambers,  canals, 

and  bones. 

20.  Tympanum  and  small  bones  of  the  ear,  twice  the  natural  size ;  a. 

tympanum ;  m,  malleus  ;  n,  incus  ;  «?,  orbiculare :  s,  stapes. 
21    Section  of  the  brain  of  a  crow,  showing  the  origin  of  the  nerves  of 
the  special  senses. 

22.  Diagram  of  the  larynx,  in  man. 

23.  Larynx  of  the  merganser,  (Mergus  merganser.) 

24.  Nests  of  Ploceus  Philippinus,  male  and  female. 

25.  Distribution  of  nerves  to  the  muscular  fibres. 

26.  Test,  or  crust-like  covering  of  an  Echinoderra,  (Cidarts.) 


EXPLANATION    OF    THE    FIGURES.  13 

Fio 
$7.  Muscular  ribbons  of  the  willow-moth>  ( Cossw  ligniperda. ) 

28.  Vertebra  of  a  cod-fish. 

29.  Disposition  of  the  muscles  of  the  trout,  (Salmo  trutta.) 

30.  Disposition  of  the  muscles  of  an  owl,  (Strix  brachyotis.) 

31.  Jelly-fishes,  (Stomobrachium  cruciatum,  Hippocrene  Bougaimrittv*} 

32.  Leech,  showing  the  terminal  cups. 

33.  Portion  of  a  Nereis,  showing  the  gills  as  organs  of  motion. 
34-43.  Modifications  of  the  fore-arm. 

34.    Monkey.     35.    Deer.     36.    Tiger.     37.    Whale.     38.    Bat. 
39.  Pigeon.    40.  Turtle.    41.  Sloth.    42.  Mole.    43.  Whale. 

44,  Leg  of  a  beetle. 

45.  Leg  of  a  lizard. 

46  Skeleton  of  a  tiger. 

47  Cuttle-fish,  (Loliyo  illecebrosa.) 

48  Sea-anemone,  (Actinia  marginata-)  a,  mouth ;  6,  stomach ;  c,  general 

cavity  of  the  body. 

49.  Planaria,  showing  the  mouth,  stomach,  and  its  branches. 

50.  Jaws,  stomach,  and  intestine  of  a  sea-urchin,  (Echinus  lividus.) 

61.  Plan  of  the  digestive  organs  of  an  insect. 

62.  Plan  of  the  digestive  organs  of  a  land-slug,  ( Tebennophorus  Carolina 

ensis.) 

53.  Globules  of  chyle. 

54.  Portion  of  intestine,  showing  the  lacteals  of  man,  and  their  entrance 

into  a  vein. 

55.  Jaws  of  an  Echinoderm,  (Echinarachnius  parma 

56.  Jaws  of  a  sea-urchin,  (Echinus  granulatus.) 

57.  Beak  of  a  cuttle-fish. 

58.  Portion  of  the  tongue  of  a  mollusk,  (Natica  heros,)  magnified. 

59.  Jaws  of  an  Annelide,  (Nereis.) 

60.  Trophi  (organs  for  taking  food)  of  a  beetle. 

61.  "      of  a  bee. 

62.  63.  "      of  a  squash-bug. 

64.  "      of  a  butterfly. 

65.  "      of  a  Rotifer,  (Brachionus.) 

66.  Jaws  of  ditto,  magnified. 

67.  Skull  of  a  tiger,  showing  the  muscles  for  mastication. 

68.  Head  of  a  snapping-turtle,  (Emysaurus  serpentina.) 

69.  Head  of  a  Whale,  showing  the  whalebone. 

70.  Head  of  an  ant-eater. 

71.  Head  of  an  alligator. 

72.  Head  of  a  skate-fish,  (Mijliobatis,')  showing  the  palate  bcne. 

73.  Head  of  a  monkey,  showing  the  three  different  kinds  of  teeth. 

74.  Teeth  of  an  insectivorous  animal,  the  mole. 

75.  Teeth  of  a  carnivorous  animal,  the  tiger. 

76.  Teeth  cf  a  rodent 


14  EXPLANATION  OF  THE  FIGURES 

PIG. 

77.  A  polyp,  ( Tubularia  indimsa ;)  m,  mouth;  o,  ovaries;//.  tantaoT??. 

78.  Blood  disks  in  man,  magnified. 

79.  "        "        in  birds,        " 

80.  "        "       'in  reptiles,    " 

81.  "        "        in  fishes,       " 

82    Porti  on  of  a  vein  opened,  to  show  *he  valves 

83.  Network  of  capillary  vessels. 

84.  Dorsal  vessel  of  an  insect,  with  its  valves. 
85    Cavities  of  the  heart  of  mammals  and  birds. 

86.  "  "        "       of  a  reptile. 

87.  "  "        "       of  a  fish. 

88.  Heart  and  bloodvessels  of  a  gasteropod  mollusk,  (Natica.) 
80,  Trachese,  or  air  tubes  of  an  insect ;  *,  stigmata ;  t,  trachea. 

90.  Relative  position  of  the  heart  and  lungs  in  man. 

91.  Respiratory  organs  of  a  naked  mollusk,  (Polycera  illuminata  ) 

92.  Respiratory  organs  (gills)  of  a  fish. 

93.  Vesicles  and  canals  of  the  salivary  glands. 

94.  Section  of  the  skin,  magnified,  to  show  the  sweat  glands  ;  a,  the  cut  • 

ft.  blood-layer  ;  c,epidermis  ;  g,  gland  imbedded  in  the  fat-layer,^ 

95.  Egg  of  a  skate-fish,  (Myliobatis.) 

96.  Egg  of  hydra. 

97.  Egg  of  snow-flea,  (Podurella.) 

98.  Section  of  an  ovarian  egg ;  d,  germinative  dot ;  g,  germinative  vesi 

cle ;  s,  shell  membrane ;  v,  vitelline  membrane. 

99.  Egg  cases  of  Pyrula. 

100.  Monoculus  bearing  its  eggs,  a  a. 

101.  Section  of  a  bird's  egg ;  a,  albumen  ;  c,  chalaza ;  et  embryo ;  s,  shell 

y,  yolk. 

102.  Cell-layer  of  the  germ. 

103.  Separation  of  the  cell-layer  into  three  layers  ;  s,  serous  or  nervou; 

layer ;  m,  mucous  or  vegetative  layer ;  v,  vascular  or  blood  layer. 

104.  Embryo  of  a  crab,  showing  its  incipient  rings. 

105.  Embryo  of  a  vertebrate,  showing  the  dorsal  furrow. 

106—8.  Sections  of  the  embryo,  showing  the  formation  of  the  dorsal  canaL 
109.  Section,  showing  the  position  of  the  embryo  of  a  vertebrate,  in  re- 
lation to  the  yolk. 

110  Section,  showing  the  same  in  an  articulate,  (Podurella.) 

111  -22.  Sections,  showing  the  successive  stages  of  development  of  the 

embryo  of  the  white-fish,  magnified. 
123    Young  white-fish  just  escaped  from  the  egg,  with  the  yolk  not  yet 

fully  taken  in. 
124,  125.  Sections  of  the  embryo  of  a  bird,  showing  the  formation  of  the 

allantois  ;  e,  embryo  ;  x  x,  membrane  rising  to  form  the  amnios ; 

a,  allantois  ;  y,  yolk. 
126.  The  same  more  fully  developed.     The  allantois  (a)  >s  further  de- 


EXPLANATION    OF    THE    FIGURES.  15 

Fio. 

veloped,  and  bent  upwards.  The  upper  part  of  the  yol*  (d  d )  is 
nearly  separated  from  the  yolk  sphere,  and  is  to  become  the  in 
testine.  The  heart  (h)  is  already  distinct,  and  connected  by 
threads  with  the  blood-layer  of  the  body. 

127.  Section  of  the  egg  of  a  mammal ;  v,  the  thick  vitelline  membrane, 

or  chorion  ;  y,  yolk ;  s,  germinative  dot ;  g,  germinative  vesicle. 

128.  The  same,  showing  the  empty  space  (k)  between  the  vitelline  sphere 

and  chorion. 

129.  Shows  the  first  indications  of  the  germ  already  divided  in  two  layers, 

the  serous  layer,  (s,)  and  the  mucous  layer,  (m.) 

130.  The  mucous  layer  (m)  expands  over  nearly  half  of  the  yolk,  and  be- 

comes covered  with  many  little  fringes. 

131.  The  embryo  (e)  is  seen  surrounded  by  the  amnios,  (b,)  and  covered 

by  a  large  allantois,  (a;)  p  e,  fringes  of  the  chorion ;  p  m,  fringes 
of  the  matrix. 

132.  Hydra,  showing  its  reproduction  by  buds. 

133.  Vorticella,  showing  its  reproduction  by  division. 

134.  Polyps,  showing  the  same. 

135.  A  chain  of  Salpae. 

136.  An  individual  salpa  ;  m,  the  mouth ;  a,  embryos 

137.  Cercaria,  or  early  form  of  the  Distoma. 

138.  Distoma,  with  its  two  suckers. 

139.  Nurse  of  the  Cercaria. 

140.  The  same,  magnified,  showing  the  included  young. 

141.  Grand  nurses  of  the  Cercaria,  enclosing  the  young  nurses. 

142.  Stages  of  development  of  a  jelly-fish,  (Medusa ;)  o,  the  embryo  in 

its  first  stage,  much  magnified ;  6,  summit,  showing  the  mouth ; 
C;/»  ff,  tentacles  shooting  forth ;  e,  embryo  adhering,  and  form- 
ing a  pedicle ;  h,  i,  separation  into  segments ;  d,  a  segment  be- 
come free ;  kt  form  of  the  adult. 

143.  Portion  of  a  plant-like  polyp,  (Campanularia,  )  a,  the  cup  which 

bears  tentacles  ;  b,  the  female  cup,  containing  eggs  ;  ct  the  cups 
in  which  the  young  are  nursed,  and  from  which  they  issue. 

144.  Young  of  the  same,  with  its  ciliated  margin,  magnified. 

145.  Eye  of  the  perch,  containing  parasitic  worms,  (Distoma.) 

146.  One  of  the  worms  magnified. 

147.  Transformations  of  the  canker-worm,  (Geometra  vemalis ;)  a,  the 

canker  worm  ;  b,  its  chrysalis  ;  c,  female  moth ;  d,  male  moth. 

148.  Metamorphoses  of  the  duck-barnacle,  (Anatifa;)  a,  eggs,  magnified; 

b,  the  animal  as  it  escapes  from  the  egg  ;  c,  the  stem  and  eye  ap- 
pearing, and  the  shell  enclosing  them  ;  d,  animal  removed  from 
the  shell,  and  further  magnified ;  e,f,  the  mature  barnacle,  affixed. 

149.  Metamorphoses  of  a  star-fish,  (Echinaster  sanguinolentus,}  showing 

the  changes  of  the  yolk,  (e  ;)  the  formation  of  the  pedicle,  {/»;) 
and  the  gradual  change  into  the  pentagonal  and  rayed  form. 


16  EXPLANATION    OF    THE    FIGURES. 

FlO. 

150.  Cornatula,  a  "West  India  species,  in  its  early  stage,  with,  its  stem 

151.  The  same  detached,  and  swimming  free. 

152.  Longitudinal  section  of  the  sturgeon,  to  show  its  cartilaginous  ver 

tebral  column. 

153.  Amphioxus,  natural  size,  showing  its  imperfect  organization. 

154.  Section  of  the  earth's  crust,  to  show  the  relative  positions  of  the 

rocks  composing  it ;  E,  plutonic  or  massive  rocks  ;  M,  metamor- 
phic  rocks  ;  T,  trap  rocks  ;  L,  lava.  1.  Lower  Silurian  forma- 
tion ;  2.  Upper  Silurian ;  3.  Devonian ;  4.  Carboniferous ;  5. 
Trias,  or  Saliferous  ;  6.  Oolitic  ;  7.  Cretaceous ;  8.  Lower  Terti- 
ary or  Eocene ;  9.  Upper  Tertiary,  or  Miocene,  and  Pleiocene ; 
10.  Drift. 

155.  Fossils  of  the  Palaeozoic  age  ;  a,  Lingula  prima  ;  b,  Leptsena  alter- 

nata  ;  c,  Euomphalus  hemisphericus  ;  d,  Trocholites  ammonius ; 
e,  Avicula  decussata ;  ft  Bucania  expansa ;  g,  Orthoceras  fusi 
forme  ;  i,  Cyathocrinus  ornatissimus,  Hall ;  j,  Cariocrinus  orna- 
tus,  Say ;  k,  Melocrinus  amphora,  Goldf. ;  I,  Columnaria  alveo , 
lata ;  m,  Cyathophyllum  quadrigeminum,  Goldf. ;  n,  o,  Caninia 
flexuosa ;  p,  Chaetetes  lycoperdon. 

156.  Articulata  of  the  Pakeozoic  age  ;  a,  Harpes  ;  b,  Arges  ;  c,  Brontes  , 

dt  Platynotus  ;  e,  Euryptei;us  remipes. 

157.  Fishes  of  tbe  Palaeozoic  age ;   a,  Pterichthys ;  b,  Coccosteus ;  ct 

Dipterus  ;  d,  palatal  bone  of  a  shark  ;  et  spine  of  a  shark. 

158.  Representations  of  the  tracks  of  supposed  birds  and  reptiles  in  the 

sandstone  rocks. 

159.  Supposed  outlines  of  Ichthyosaurus,  (a,)  and  Plesiosaurus,  (b.) 

160.  Supposed  outline  of  Pterodactyle. 

161.  Shells   of  the  Secondary  age;    a,   Terebratula;  b,  Goniomya;  c, 

Trigonia ;   d,  Ammonite. 

162.  Supposed  outline  of  the  cuttle-fish,  (a,)  furnishing  the  Belemnite. 

163.  Radiata  from  the  Secondary  age  ;  a,  Lobophyllia  flabellum  ;  b,  Litho- 

dendron  pseudostylina ;  c,  Pentacrinus  briareus  ;  d,  Pterocoma 
pinnata ;  e,  Cidaris  ;  ft  Dysaster ;  g,  Nucleolites. 

164.  Shells  of  the  Cretaceous  formation ;  a,  Ammonites ;  b,  Criocerns  j 

c,  Scaphites ;  d,  Ancyloceras ;  e,  Karaites  ;  /,  Baculites ;  g, 
Turrilites. 

165.  Shells  of  the  Cretaceous  formation ;  a,  Magas ;  5,  Inoceramus ;  £>, 

Hippurites  ;   d,  Spondylus  ;   e,  Pleurotomaria. 

166.  Radiata  from  the  Cretaceous  formation ;  a,  Diploctenium  cordatura 

6,  Marsupites ;    d,    Galerites ;    c,   Salenia ;    e    Micraster    con 

anguinum. 
167   Nummulite. 
168.  Supposed  outline  of  Paleotherium. 

169  Supposed  outline  of  Anoplotherium. 

170  Skeleton  of  the  Mastodon,  in  the  cabinet  of  Dr.  J.  C.  Warren. 


INTRODUCTION. 


EVERY  art  and  science  has  a  language  of  technical  terms 
peculiar  to  itself.  With  those  terms  every  student  must 
make  himself  familiarly  acquainted  at  the  outset ;  and,  firsi 
of  all,  he  will  desire  to  know  the  names  of  the  objects  about 
which  he  is  to  be  engaged. 

The  names  of  objects  in  Natural  History  are  double ;  that 
is  to  say,  they  are  composed  of  two  terms.  Thus,  we  speak 
of  the  white-bear,  the  black-bear,  the  hen-hawk,  the  sparrow- 
hawk  ;  or,  in  strictly  scientific  terms,  we  have  Fells  leo,  the 
lion,  Felis  tigris,  the  tiger,  Felis  catus,  the  cat,  Canis  lupus, 
the  wolf,  Canis  vulpes,  the  fox,  Canis  familiaris,  the  dog, 
&c.  They  are  always  in  the  Latin  form,  and  consequently 
the  adjective  name  is  placed  last.  The  first  is  called  the 
generic  name ;  the  second  is  called  the  trivial,  or  specific 
name. 

These  two  terms  are  inseparably  associated  in  every 
object  of  which  we  treat.  It  is  very  important,  therefore 
'to  have  a  clear  idea  of  what  is  meant  by  the  terms  genus  and 
species  ;  and  although  the  most  common  of  all  others,  they 
are  not  the  easiest  to  be  clearly  understood.  The  Genus  is 
2* 


18  INTRODUCTION. 

ibunded  upon  some  of  the  minor  peculiari/ies  of  anat.raica. 
structure,  such  as  the  number,  disposition,  or  proportions 
of  the  teeth,  claws,  fins,  &c.,  and  usually  includes  several 
kinds.  Thus,  the  lion,  tiger,  leopard,  cat,  &c.,  agree  in  the 
structure  cf  their  feet,  claws,  and  teeth,  and  they  belong  to 
the  genus  Felis ;  while  the  dog,  fox,  jackal,  wolf,  &c.,  have 
another  and  a  different  peculiarity  of  the  feet,  claws,  and 
teeth,  and  are  arranged  in  the  genus  Canis. 

The  Species  is  founded  upon  less  important  distinctions, 
such  as  color,  size,  proportions,  sculpture,  &c.  Thus  we 
have  different  kinds,  or  species,  of  duck,  different  species 
of  squirrel,  different  species  of  monkey,  &c.,  varying  from 
each  other  in  some  trivial  circumstance,  while  those  of  each 
group  agree  in  all  their  general  structure.  The  specific 
name  is  the  lowest  term  to  which  we  descend,  if  we  except 
certain  peculiarities,  generally  induced  by  some  modification 
of  native  habits,  such  as  are  seen  in  domestic  animals. 
These  are  called  varieties,  and  seldom  endure  beyond  the 
causes  which  occasion  them. 

Several  genera  which  have  certain  traits  in  common  are 
combined  to  form  a  family.  Thus,  the  ale  wives,  herrings, 
shad,  &c.,  form  a  family  called  Clupeidse ;  the  crows,  black- 
birds, jays,  &c.,  form  the  family  Corvidse.  Families  are 
combined  to  form  orders,  and  orders  form  classes,  and  finally, 
classes  are  combined  to  form  the  four  primary  divisions  or 
departments,  of  the  Animal  Kingdom. 

For  each  of  these  groups,  whether  larger  or  smaller,  \ve 
involuntarily  picture  in  our  minds  an  image,  made  up  of  the 
traits  which  characterize  the  group.  This  ideal  image  is 
called  a  TYPE,  a  term  which  there  will  be  frequent  occasion 
to  employ  in  our  general  remarks  on  the  Animal  Kingdom. 
This  image  may  correspond  to  some  one  member  of  the 
group  ;  but  it  is  rare  that  any  one  species  embodies  all  our 
•deas  of  the  class,  family,  or  genus  to  which  it  belongs. 


INTRODUCTION.  19 

Thus,  we  have  a  general  idea  of  a  bird  ;  but  this  idea  does 
not  correspond  to  any  particular  bird,  or  any  particulai 
character  of  a  bird.  It  is  not  precisely  an  ostrich,  an  owl, 
a  hen,  or  a  sparrow  ;  it  is  not  because  it  has  wings,  or 
feathers,  or  two  legs ;  or  because  it  has  the  power  of  flight, 
or  builds  nests.  Any,  or  all,  of  these  characters  would  not 
fully  represent  our  idea  of  a  bird  ;  and  yet  every  one  has  a 
distinct  ideal  notion  of  a  bird,  a  fish,  a  quadruped,  &c.  It  is 
common,  however,  to  speak  of  the  animal  which  embodies 
most  fully  the  characters  of  a  group,  as  the  type  of  that 
group.  Thus  we  might,  perhaps,  regard  an  eagle  as  the 
type  of  a  bird,  the  duck  as  the  type  of  a  swimming-bird,  and 
the  mallard  as  the  type  of  a  duck,  and  so  on. 

As  we  must  necessarily  make  frequent  allusions  to  ani- 
mals, with  reference  to  their  systematic  arrangement,  it  seems 
requisite  to  give  a  sketch  of  their  classification  in  as  popular 
terms  as  may  be,  before  entering  fully  upon  that  subject,  and 
with  particular  reference  to  the  diagram  fronting  the  title- 
page. 

The  Animal  Kingdom  consists  of  four  great  divisions, 
which  we  call  DEPARTMENTS,  namely  : 

I.  The  department  of  Vertebrates. 
II.  The  department  of  Articulates. 

III.  The  department  of  Mollusks. 

IV.  The  department  of  Radiates. 


1.  The  department  of  VERTEBRATES  includes  all  animals 
which  have  an  internal  skeleton,  with  a  back-bone  for  its 
axis.  It  is  divided  into  four  classes  : 

1.  Mammals,  (animals  which  nurse  their  young.) 

2.  Birds. 


INTRODUCTION. 


3.  Reptiles. 

4.  Fishes. 


The  class  of  MAMMALS  is  subdivided  into  three  orders  •, 
a    Beasts  of  prey,  ( Carnivora.) 
b    Those  which  feed  on  vegetables,  (Herlivora.) 
c.  Animals  of  the  whale  kind,  (Cetaceans.) 

The  class  of  BIRDS  is  divided  into  four  orders,  namely, 

a.  Perching  Birds,  (Insessores.) 

b.  Climbers,  (Scansores.) 

c.  Waders,  (Grallatores.) 

d.  Swimmers,  (Natatores.) 

The  class  of  REPTILES  is  divided  into  five  orders : 

a.  Large  reptiles  with  hollow  teeth,  most  of  which  are 

now  extinct,  (Rhizodonts.) 

b.  Lizards,  (Lacertians.) 

c.  Snakes,  ( Ophidians.) 

d.  Turtles,  (Chelonians.) 

e.  Frogs  and  Salamanders,  (Batrachians.) 

The  class  of  FISHES  is  divided  into  four  orders  : 

a.  Those   with   enamelled   scales,   like    the    gar-pike, 

(Ganoids,)  fig.  157,  c. 
ft.  Those  with  the  skin  like  shagreen,  as  the  sharks  and 

skates,  (Placoids.) 
c.  Those  which  have  the  edge  of  the  scales  toothea, 

and  usually  with  some  bony  rays  to  th?  iins,  as  the 

perch,  ( Ctenoids.) 


INTRODUCTION.  21 

d.  Those  whose  scales  are  entire,  ind  whose  fin  rays 
are  soft,  like  the  salmon,  (Cycloids.) 


II.  Department  of  ARTICULATES.     Animals  whose  body  is 
composed  of  rings  or  joints.     It  embraces  three  classes  : 

1.  Insects. 

2.  Crustaceans,  like  the  crab,  lobster,  &c. 

3.  Worms, 

The  class  of  INSECTS  includes  three  orders : 

a.  Those  with  a  trunk  for  sucking  fluids,  like  the  butter* 

fly,  (Suctoria,)  fig.  62-64. 

b.  Those  which  have  jaws  for  dividing  their  food,  (Man- 

ducata,}  fig.  60. 

c.  Those  destitute  of  wings,  like  spiders,  fleas,  millipedes 

&c.,  (Aptera.) 

The  class  CRUSTACEANS  may  be  divided  as  follows : 

a.  Those  furnished  with  a  shield,  like  the  crab  and  lob- 

ster, (Malacostraca.) 

b.  Such  as  are  not  thus  protected,  (Entomostraca.) 

c.  An  extinct  race,  intermediate  between  these   two, 

(Trilobites,)  fig.  156. 

The  class  of  WORMS  comprises  three  orders  : 

a.  Those  which  have  thread-like  gills  about  the  head, 

( Tubulilranchiates.) 

b.  Those  whose  gills  are  placed  along  the  sides,  (Dor* 

sibranchiates.) 

c.  Those  who  have  no  exterior  gills,  like  the  earth-worrn 

(Abrancliiates,)  and  also  the  Intestinal  Worms. 


22  INTRODUCTION. 

III.  The  department  of  MOLLUSXS  is  divided  into  tfirec 
classes,  namely : 

1 .  Those  which  have  arms  about  the  mouth,  like  the 

cuttle-fish,  (Cephalopods,)  fig.  47. 

2.  Those  which  creep  on  a  flattened  disk  or  foot,  like 

snails,  (Gasteropods,)  fig.  88. 

3.  Those  which  have  no  distinct  head,  and  are  inclosed 

in  a  bivalve  shell,  like  the  clams,  (Acephals.) 

The  CEPHALOPODS  may  be  divided  into 

a.  The  cuttle-fishes,  properly  so  called,  ( Teuthideans,) 

fig.  47. 

b.  Those  having  a  shell,  divided  by  sinuous  partitions 

into  numerous  chambers,  (Ammonites,)  fig.  164. 

c.  Those  having  a  chambered  shell  with  simple  par- 

titions, (Nautilus.) 

The  GASTEROPODS  contain  four  orders  : 

a.  The  land  snails  which  breathe  air,  (Pulmonates.) 

b.  The  aquatic  snails  which  breathe  water,  (Branch- 

ifers,)  fig.  88. 

c.  Those  which  have  wing-like  appendages  about  the 

head,  for  swimming,  (Pteropods.) 

d.  A  still  lower  form  allied  to  the  Polyps  by  their  gen- 

eral appearance,  (R/iizopods  or  Foraminifera.) 

The  class  of  ACEPHALS  contains  three  orders : 

a.  Those  having  shells  of  two  valves,  (bivalves,)  like  the 
clam  and  oyster,  (LamellibrancMates.) 

6.  Those  having  two  unequal  valves,  and  furnished  with 
peculiar  arms,  (Brachiopods.) 


INTRODUCTION  23 

c.  Mollusks  living  in  chains  or  clusters,  like  the  Salp;i,  fig. 
135 ;  or  upon  plant-like  stems,  like  Flustra,  (Bryo- 
zoa.) 


IV.  The  department  of  RADIATES  is  divided  into  -three 
:lasses : 

1.  Sea-urchins,  bearing  spines  upon  the  surface,  (Echin* 

odernis,)  figs.  12,  26. 

2.  Jelly-fishes,  (Acalephs,)  fig.  31. 

3.  Polyps,  fixed  like  plants,  and  with  a  series  of  flexible 

arms  around  the  mouth,  figs.  48,  77,  143. 

The  ECHINODERMS  are  divided  into  four  orders : 

a.  Sea-slugs,  like  biche-le-mar,  (Holot/iurians.) 

b.  Sea-urchins,  (Echini,)  fig.  26. 

c.  Free  star-fishes,  (Asterida,)  fig.  17. 

d.  Star-fishes  mostly  attached  by  a  stem,  (CrinoidsJ 

figs.  150,  151. 

The  ACALEPHS  include  the  following  orders : 

a.  Those  furnished  with  vibrating  hairs,  by  which  they 

move,  (Ctenophora.) 

b.  The  Medusse,  or  common  jelly-fishes,  (Discophora,) 

figs.  31,  142. 

c.  Those  provided  with  aerial  vesicles,  (Siphonophorte.) 

The  class  of  POLYPS  includes  two  orders. 

a.  The  so-called  fresh-water  polyps,  and  similar  marine 

forms,  with  lobed  tentacles,  (Hydro'ids,)  fig.  143. 

b.  Common  polyps,  like  the  sea-anemone    and   coral 

polyp,  (Actinoids,)  fig.  48. 

in  addition  to  these,  there  are  numberless  kinds  of  micro- 


24  INTRODUCTION. 

scoplc  animalcules,  commonly  united  under  the  name  of 
infusory  animals,  (Infusoria,)  from  their  being  found  specially 
abundant  in  water  infused  with  vegetable  matter.  These 
minute  beings  do  not,  however,  constitute  a  natural  group  in 
the  Animal  Kingdom.  Indeed,  a  great  many  that  were  for- 
merly supposed  to  be  animals  are  now  found  to  be  vegetables. 
Others  are  ascertained  to  be  crustaceans,  mollusks,  worms 
of  microscopic  size,  or  the  earliest  stages  of  development  ot 
larger  species.  •  In  general,  however,  they  are  exceedingly 
minute,  and  exhibit  the  simplest  forms  of  animal  life,  and 
are  now  grouped  together,  under  the  title  of  Protozoa.  But, 
as  they  are  still  very  imperfectly  understood,  notwithstand- 
ing the  beautiful  researches  already  published  on  this  sub- 
ject, and  as  many  of  them  are  likely  to  be  finally  distributed 
among  vegetables,  and  the  legitimate  classes  in  the  Animal 
Kingdom  to  which  they  belong,  we  have  not  assigned  any 
special  place  for  thorn. 


PHYSIOLOGICAL  ZOOLOGY 


A  CHAPTER    FIRST. 

THE  SPHERE  AND  FUNDAMENTAL   PRINCIPLES  OP 
ZOOLOGY. 

1.  ZOOLOGY  is  that  department  of  Natural  History  wh;c^ 
relates  to  animals 

2.  To  enumerate  and  name  the  animals  which  are  found 
on  the  globe,  to  describe  their  forms,  and  investigate  their 
habits  and  modes  of  life,  are  the  principal,  but  by  no  means 
the  only  objects  of  this  science.     Animals  are  worthy  of  our 
regard,  not  merely  when  considered  as  to  the  variety  and  ele- 
gance of  their  forms,  or  their  adaptation  to  the  supply  of  our 
wants  ;   but  the  Animal    Kingdom,  as  a  whole,  has   a  still 
higher  signification.     It  is  the  exhibition  of  the  divine  thought, 
as  carried  out  in  one  department  of  that  grand  whole  which 
ws  call  Nature ;  and  considered  as  such,  it  teaches  us  mos* 
rnportant  lessons. 

3.  Man,  in  virtue  of  his  twofold  constitution,  the  spiritual 
and    the    material,    is    qualified    to    comprehend    Nature. 

3 


26  SPHERE    AND    FUNDAMENTAL 

Being  made  .'n  the  spiritual  image  of  God,  he  is  competent  to 
rise  to  the  conception  of  His  plan  and  purpose  in  the  works 
of  Creation.  Having  also  a  material  body,  like  that  of 
other  animals,  he  is  also  in  a  condition  to  understand  the 
mechanism  of  organs,  and  to  appreciate  the  necessities  of 
matter,  as  well  as  the  influence  which  it  exerts  over  the  in- 
tellectual element  throughout  the  domain  of  Nature. 

4.  The  spirit  and  preparation  we  bring  to  the  study  of 
Nature,  is  a  matter  of  no  little  consequence.    When  we  wou'.d 
study  with  profit  a  work  of  literature,  we  first  endeavor  to 
make  ourselves  acquainted  with  the  genius  of  the  author; 
and  in  order  to  know  what  end    he  had  in  view,  we  must 
have  regard  to  his  previous  labors,  and  to  the  circumstances 
under  which  the  work  was  executed.     Without  this,  although 
we  may  perhaps  enjoy  its    perfection  as  a  whole,  and  ad- 
mire the  beauty  of  its  details,  yet  the  spirit  which  pervades 
it  will  escape  us,  and  many  passages  may  even  remain  un- 
intelligible. 

5.  So,  in  the  study  of  Nature,  we  may  be  astonished  at 
the   infinite  variety  of  her    products;    we  may  even  study 
some  portion  of  her  works  with  enthusiasm,  and  neverthe- 
less remain  strangers  to  the  spirit  of  the  whole,  ignorant  of 
the  plan  on  which  it  is  based,  and  fail  to  acquire  a  proper 
conception  of  the    varied   affinities  which   combine    beings 
together,  so  as  to  make  of  them  that  vast  picture  in  which 
each  animal,  each  plant,  each   group,  each  class,  has    its 
place,  and    from  which  nothing  could    be  removed  without 
destioying  the  proper  meaning  of  the  whole. 

6.  Besides  the  beings  which  inhabit  the  earth  at  the  pres- 
ent time,  this  picture  also  embraces  the  extinct  races  which 
are  now  known  to  us  by  their  fossil  remains  only.     And 
these  are  of  the  greatest  importance,  since  they  furnish  us 
with  the  means  of  ascertaining  the  changes  and  modifica- 
tions which  the  Animal  Kingdom  has  undergone  in  the  sue- 


PRINCIPLES*    OF    ZOOLOGY  27 

aessive    creations,   since    the    first    appearance    of    living 
beings. 

7.  It  is  but  a  short  time  since  it  was  not  difficult  for  a 
man  to  possess  himself  of  the  whole  domain  of  positive 
knowledge  in  Zoology.  A  century  ago,  the  number  of 
known  animals  did  not  exceed  8000;  that  is  to  say,  from 
the  whole  Animal  Kingdom,  fewer  species  were  then 
known  than  are  now  contained  in  many  private  collections 
of  certain  families  of  insects  merely.  At  the  present 
day,  the  number  of  living  species  which  have  been  satisfac- 
torily made  out  and  described,  is  more  than  50,000.*  The 
fossils  already  described  exceed  6000  species ;  and  if  we 

*  The  number  of  vertebrate  animals  may  be  estimated  at  20,000. 
About  1500  species  of  mammals  are  pretty  precisely  known,  and  the  num- 
ber may  probably  be  carried  to  about  2000. 

The  number  of  Birds  well  known  is  4  or  5000  species,  and  the  probable 
number  is  6000. 

The  Reptiles  number  about  the  same  as  the  Mammals,  1500  described 
species,  and  they  will  probably  reach  the  number  of  2000. 

The  Fishes  are  more  numerous  :  there  are  from  5  to  6000  species  in  the 
museums  of  Europe,  and  the  number  may  probably  amount  to  8  or  10,000. 

The  number  of  Mollusks  already  in  collections  probably  reaches  8  or 
10,000.  There  are  collections  of  marine  shells,  bivalve  and  univalve,  which 
amount  to  5  or  6000 ;  and  collections  of  land  and  fluviatile  shells,  which 
count  as  many  as  2000.  The  total  number  of  mollusks  would,  therefore, 
probably  exceed  15,000  species. 

Among  the  articulated  animals  it  is  difficult  to  estimate  the  number  of 
species.  There  are  collections  of  coleopterous  insects  which  number  20  la 
25,000  species  ;  and  it  is  quite  probable,  that  by  uniting  the  principal  cd 
lections  of  insects,  60  or  80,000  species  might  now  be  counted;  f*.r  the 
whole  department  of  artieulata,  comprising  the  Crustacea,  the  eirrhipeda, 
the  insects,  the  red-blooded  worms,  the  intestinal  worms,  and  the  infuso- 
ria so  far  as  they  belong  to  this  department,  the  number  would  already 
amount  to  100,000 ;  and  we  might  safely  compute  the  probable  number  of 
sf  ecies  actually  existing  at  double  that  sum. 

Add  to  these  about  10,000  for  radiata,  including  echini,  star-fishes,  me- 
dusa;, and  polypi,  and  we  have  about  250,000  species  of  living  animals  ;  and 
supposing  the  number  of  fossil  species  only  to  equal  them,  we  b'<  ve,  at  » 
veiy  moderate  computation,  half  a  million  of  species. 


28  SPHERE   AND   FUNDAMENTAL 

consider  that  whatever  any  one  stratum  of  the  eaiJi  has 
been  well  explored,  the  number  of  species  discovered  has 
not  fallen  below  that  of  the  living  species  which  now  inhabit 
any  particular  locality  of  equal  extent,  and  then  bear  in 
mind  that  there  is  a  great  number  of  geological  strata,  we 
may  anticipate  the  day  when  the  ascertained  fossil  species 
will  far  exceed  the  living  species.* 

8.  These  numbers,  far  from  discouraging,  should,  on  the 
contrary,    encourage    those    who    study    Natural    History. 
Each   new   species  is,  in  some  respects,  a   radiating   point 
which  throws  additional  light  on  all  around  it ;  so  that,  as 
the  picture  is  enlarged,  it  at  the  same  time,  becomes  more 
:ntelligible  to  those  who  are  competent  to  seize  its  promi- 
nent traits. 

9.  To  give  a  detailed  account  of  each  and  all  of  these 
animals,  and  to  show  their  relations  to  each   other,  is  the 
task  of  the  Naturalist.     The  number  and  extent  of  the  vol- 
umes already  published   upon  the  various  departments  of 
Natural  History  show,  that  only  a  mere  outline  of  a  domain 
so  vast  could  be  fully  .sketched  >in  an  elementary  work,  and 
that  none  but  those  who  make  it  their  special  study  can  be 
expected  to  survey  its  individual  parts. 

10.  Every  well-educated  person,  however,  is  expected  tc 
have  a  general  acquaintance  with  the    great  natural    phe- 
nomena constantly  displayed  before  his  eyes.     There  is  a 
general    knowledge  of  man    and   the  subordinate   animals* 
embracing  their  structure,  races,  habits,  distribution,  mutual 
relations,  &c.,  which  is  not  only  calculated  to  conduce  es- 


*  In  a  separate  work,  entitled  "  Nomenclator  ZoOlogictts,"  by  L.  AGAS- 
8iz,  the  principles  of  nomenclature  are  discussed,  and  a  list  of  the  names 
of  genera  and  families  proposed  by  authors  is  given.  To  this  work  those 
are  referred  who  may  desire  to  become  more  familiar  with  nomenclature, 
and  to  ki  cw  in  detail  the  genera  and  families  in  each  class  of  the  Animal 
Kingdom 


PRINCIPLES    OF    ZOOLOGY.  29 

sentially  to  our  happiness*  but  which  it  would  be  quite  inex- 
cusable to  neglect.  This  general  view  of  Zoology,  «t  is  the 
purpose  of  this  work  to  afford. 

11.  A  sketch  of  this  nature  should  render  prominent  the 
more  general  features  of  animal   life,  and  delineate  the  ar- 
rangement of  the  species  according  to  their  most  natural 
relations  and  their  rank  in  the  scale  of  being  ;  thus  giving 
a  panorama,  as   it  were,   of  the  entire  Animal   Kingdom, 
To  accomplish  this,  we  are  at  once  involved  in  the  question. 
What  is  it  that  gives  an  animal  precedence  in  rank  ? 

12.  In  one  sense,  all  animals  are  equally  perfect.     Each 
pecies  has  its  definite  sphere   of  action,  whether  more  or 

less  extended,  —  its  own  peculiar  office  in  the  economy  of 
nature  ;  and  a  complete  adaptation  to  fulfil  all  the  purposes 
of  its  creation,  beyond  the  possibility  of  improvement.  In 
this  sense,  every  animal  is  perfect.  But  there  is  a  wide 
difference  among  them,  in  respect  to  their  organization.  In 
some  it  is  very  simple,  and  very  limited  in  its  operation  ;  in 
others,  extremely  complicated,  and  capable  of  exercising  a 
great  variety  of  functions,  y 

13.  In  this  physiological  point  of  view,  an  animal  may  be 
xsaid  to  be  more  perfect  in  proportion  as  its  relations  with  the 

external  world  are  more  varied  ;  in  other  words,  the  more 
numerous  its  functions  are.  Thus,  an  animal,  like  a  quad- 
ruped, or  a  bird,  which  has  the  five  senses  fully  developed, 
and  which  has,  moreover,  the  faculty  of  readily  trans- 
porting itself  from  place  to  place,  is  more  perfect  than  a 
snail,  whose  senses  are  very  obtuse,  and  whose  motion  is 
very  sluggish. 

14.  In  like  manner,  each  of  the  organs,  when  separately 
considered,  is  found  to  have  every  degree  of  complication, 
and,   consequently,  every  degree  of  nicety  in  the  perform- 
ance of  its  function.     Thus,  the  eye-spots  of  the  star-fish 
and  jelly-fish  are  probably  endowed  with  merely  the  fac 

3* 


30  SPHERE    AND    FUNDAMENTAL 

ulty  of  perceiving  light,  without  the  power  of  distinguishing 
objects.  The  keen  eye  of  the  bird,  on  the  contrary,  dis- 
cerns minute  objects  at  a  great  distance,  and  when  compared 
with  the  eye  of  a  fly,  is  found  to  be  not  only  more  perfect, 
but  constructed  on  an  entirely  different  plan.  It  is  the 
same  with  every  other  organ. 

15.  We  understand  the  faculties  of  animals,  and  appre- 
ciate their  value,  just  in  proportion  as  we  become  acquainted 
with  the  instruments  which  execute  them.     The  study  of 
the  functions  or  uses  of  organs,  therefore,  requires  an  exam- 
ination  of  their   structure ;   they   must  never  be  disjoined, 
and  must  precede  the  systematic  distribution  of  animals  into 
classes,  families,  genera,  and  species. 

16.  In  this  general  view  of  organization,  we  must  ever 
bear  in  mind  the   necessity  of  carefully  distinguishing  be- 
tween affinities  and   analogies,  a  fundamental  principle  re- 
cognized even  by  Aristotle,  the  founder  of  scientific  Zoology. 
Affinity  or  homology  is  the  relation  between  organs  or  parts 
of  the  body  which  are  constructed  on   the  same  plan,  how- 
ever much  they  vary  in  form,  or  even  serve  for  very  dif- 
ferent uses.     Analogy,  on  the  contrary,  indicates  the  simi- 
larity of  purposes  or  functions  performed  by  organs  of  dif- 
ferent structure. 

17.  Thus,  there  is  an  analogy  between  the  wing  of  a  bird 
and  that  of  a  butterfly,  since   both  of  them  serve  for  flight. 
But  there  is  no  affinity  between  them,  since,  as  we  shall 
hereafter  see,  they  differ  totally  in  their  anatomical  relations. 
On   the  other  hand,  there  is  an  affinity  between  the  bird's 
wing  and  the  hand  of  a  monkey  ;  since,  although  they  serve 
for    different   purposes,   the   one    for  flight,   and    the  other 
for  climbing,  they  are  both  constructed  on  the  same  plan. 
Accordingly,  the  bird  is  more  nearly  "allied  to  the  monkey 
than  to   the  butterfly,  though  they   both  have    in    common 
the  faculty  of  flight.     Affinities,  and  not  analogies,  therefore, 
must  g'lide  us  in  the  arrangement  of  animals. 


PRINCIPLES    OF    ZOOLOGY.  81 

18.  Our   investigations   should    not    be    limited   to   adul 
ajimals,  but  should  also  include    the  changes  which   they 
undergo  during    the   whole   course   of   their    development. 
Otherwise,  we  shall  be  liable  to  exaggerate  the  importance 
of  certain  peculiarities  of  structure  which  have  a  predomi- 
nant character  in  the  full-grown  animal,  but  which  are  shaded 
off,  and  vanish,  as  we  revert  to  the  earlier  periods  of  life. 

19.  Thus,  for  example,  by  regarding  only  adult  individu- 
als, we  might   be   induced  to  divide  all    animals  into  two 
groups,  according  to  their  mode  of  respiration  ;  uniting,  on 
the  one  hand,  all  those  which  breathe  by  gills,  and,  on  the 
other,  those  which   breathe  by  lungs.     But  this  distinction 
loses  its  importance,  when  we  consider  that  various  animals, 
for   example,   frogs,  which   respire    by  lungs  in  the  adult 
state,  have  only  gills  when  young.     It  is  thence  evident  thai 
the   respiratory  organs  cannot   be  taken   as  a   satisfactorj 
basis  of  our  fundamental  classification.     They  are,  as  we 
shall  see,  subordinate  to  a  more  important  system,  namely, 
the  nervous  system. 

20.  Again,  we  have  a  means  of  appreciating  the  relative 
grade  of  animals  by  the  comparative  study  of  their  devel- 
opment.    It  is  evident  that  the  caterpillar,  in   becoming  a 
butterfly,  passes  from  a  lower  to  a  higher  state.     Clearly, 
therefore,  animals  resembling  the  caterpillar,  the  worms,  for 
instance,  must  occupy  a  lower  rank  than  those  approaching 
the  butterfly,  like  most  insects.     There  is  no  animal  which 
does  not  undergo  a  series  of  changes  similar  to  those  of  t!ie 
caterpillar  or  the  chicken  ;  only,  in  many  of  them,  the  most 
important  ones  occur  before  birth,  during  what  is  called  the 
embryonic  period. 

21.  The  life  of  the  chicken  has  not  just  commenced  when 
it  issues  from  the  egg  ;  for  if  we   break  the  egg  some  days 
previous  to  the  time  of  hatching,  we  find  in  it  a  living  ani- 
mal, which,  although  imperfect,  is  nevertheless  a  chicken  • 


'42  SPHERE    AND    FUNDAMENTAL 

it  lias  been  developed  from  a  hen's  egg,  and  we  know  thai, 
should  it  continue  to  live,  it  would  infallibly  display  all  the 
characteristics  of  the  parent  bird.  Now,  if  there  existed  in 
Nature  an  adult  bird  as  imperfectly  organized  as  the  chicken 
on  the  day,  or  the  day  before  it  was  hatched,  we  should 
assign  to  it  an  inferior  rank. 

22.  In  studying  the  embryonic   states  of  the  mollusks  or 
worms,  we  observe  in  them  points  of  resemblance  to  many 
animals  of  a   lower   grade,  to  which    they    at    length    be- 
come  entirely    dissimilar.      For  example,  the   myriads    of 
minute  aquatic  animals  embraced   under  the  name  of  Infu- 
soria, generally  very   simple  in  their  organization,  remind 
us  of  the  embryonic  forms  of  other  animals.     We  shall  have 
occasion  to  show  that  the  Infusoria  are  not  to  be  considered 
as  a  distinct  class  of  animals,  but  that  among  them  are  found 
members    of  all    the    lower    classes   of   animals,    mollusks, 
crustaceans,  worms,  &c. ;  and  many  of  them  are  even  found 
to  belong  to  the  Vegetable  Kingdom. 

23.  Not  less  striking  are  the  relations  that  exist  between 
animals  and  the  regions  they  inhabit.     Every  animal  has  its 
home.     Animals  of  the  cold  regions  are   not  the  same  as 
those  of  temperate  climates:  and  these  latter,  in  thei>*  turn, 
differ  from  those  of  tropical  regions.     Certainly,  no  one  will 
maintain  it  to  be   the  effect  of  accident  that  the   monkeys, 
the  most  perfect  of  all  brute  animals,  are  found  only  in  hot 
countries  ;    or  that  by  chance  merely  the  white   bear  and 
reindeer  inhabit  only  cold  regions. 

24.  Nor  is  it  by  chance  that  most  of  the  largest  animals, 
of  every  class,  the  whales,  the  aquatic  birds,  the  sea-turtles, 
the  crocodiles,  dwell  in  the  water  rather  than  on  the  land. 
And  while  the  water  affords  freedom  of  motion  to  the  largest, 
it  is  also  the  home  of  the  smallest  of  living  beings,  allow- 
ing a  degree  of  liberty  to  their  motion,  which  they  could  nol 
enjoy  elsewhere. 


VK1NCIPLES    OI     ZOOLOGY.  33 

25.  Nor  are  3ur  researches  to  be  limited  to  the  animals 
now  living.     There  are  buried  in  the  crust  of  the  earth  the 
remains   of  a  great  number  of  animals  belonging  to  species 
which    do  not   exist   at   the   present  day.     Many  of  those 
remains  present  forms  so  extraordinary  that  it  is  almost  im- 
possible   to  trace    their    alliance    with    any  animal    now 
living.     In  general,  they  bear  a  striking  analog}'  to  the  em- 
bryonic forms  of  existing  species.     For  example,  the  curi- 
ous fossils  known  under  the  name  of  Trilobites  (Fig.  156) 
have  a  shape  so  singular  that  it  might  well  be  doubted  to 
what  group  of  articulated  animals  they  belong.     But  if  we 
compare  them  with  the  embryo  crab,  we  find  so  remarkable 
a  resemblance  that  we  do  not  hesitate  to  refer  them  to  the 
crustaceans.     We  shall  also  see  tha.  some  of  the   Fishes 
of  ancient  epochs  present  shapes  altogether  peculiar  to  them- 
selves, (Fig.  157,)  but  resembling,  in  a  striking  manner,  the 
embryonic  forms  of  our  common  fishes.     A  determination 
of  the  successive  appearance  of  animals  in  the  order  of  time 
is,  therefore,  of  much  importance  in  assisting  to  decide  the 
relative  rank  of  animals. 

26.  Besides  the  distinctions  to  be  derived  from  the  varied 
structure  of  organs,  there  are   others   less  subject  to  rigid 
analysis,  but  no  less  decisive,  to  be  drawn  from  the  imma- 
terial principle  with  which  every  animal  is  endowed.     It  is 
this  which  determines  the  constancy  of  species  from  genera- 
tion to  generation,  and  which  is  the  source  of  all  the  varied 
exhibitions  of   instinct  and   intelligence  which   we  see  dis- 
played, from  the  simple  impulse  to  receive  the  food  which  is 
brought  within  their  reach,  as  observed  in  the  polyps,  through 
the  higher  manifestations,  in  the  cunning  fox,  the  sagacious 
elephant,  the  faithful  dog,  to  the  exalted  intellect  of  man, 
which  is  capable  of  indefinite  expansion. 

27.  Such  are  some  of  the  general  aspects  in  which  we  • 
are  to  contemplate    the  animal  creation.      Two   points  of 


34  FUNDAMENTAL    PRINCIPLES    OF    ZOOLOGY. 

view  should  never  be  lost  sight  of,  nor  disconnected,  namely, 
the  animal  in  respect  to  its  own  organism,  and  the  animal 
in  its  relations  to  creation  as  a  whole.  .  By  adopting  too 
exclusively  either  of  these  points  of  view,  we  are  in  danger 
of  falling  either  into  gross  materialism,  or  into  vague  and 
profitless  pantheism.  He  who  beholds  in  Nature  nothing 
besides  organs  and  their  functions,  may  persuade  himself 
that  the  animal  is  merely  a  combination  of  chemical  and 
mechanical  actions  and  reactions,  and  thus  becomes  a  mate- 
rialist. 

28.  On  the  contrary,  he  who  considers  only  .the  manifes- 
tations of  intelligence  and   of  creative  will,  without  taking 
into  account  the  means  by  which  they  are  executed,  and  the 
physical  laws  by  virtue  of  which  all  beings  preserve  their 
characteristics,  will  be  very  likely  to  confound  the  Creator 
with  the  creature. 

29.  It  is  only  as  it  contemplates,  at  the  same  time,  matter 
and  mind,  that  Natural   History  rises  to  its  true  character 
and  dignity,  and  leads  to  its  worthiest  end,  by  indicating  to 
us,  in  Creation,  the  execution  of  a  plan  fully  matured  in  the 
beginning,  and  undeviatingly  pursued  ;  the   work  of  a  God 
infinitely  wise,  regjlating  Nature  according  to  imrni  table 
laws,  which  He  has  himself  imposed  on  her. 


CHAPTER    SECOND. 

GENERAL  PROPERTIES  OF  ORGANIZED  BODIES 
SECTION  I. 

ORGANIZED    AND     UNORGANIZED     BODIES. 

30.  NATURAL  HISTORY,  in  its  broadest  sense,  embraces 
the  study  of  all  the  bodies  which  compose  the  crust  of  the 
earth,  or  which  are  dispersed  over  its  surface. 

31.  These  bodies  may  be  divided  into  two  great  groups  ; 
inorganic  bodies,  (minerals  and  rocks,)  and  living  or  organ- 
ized bodies,  (vegetables  and   animals.)     These  two  groups 
have  nothing  in  common,  save  the  universal   properties  of 
matter,  such  as  weight,  extension,  &c.     They  differ  at  the 
same  time   as  to  their  form,  their  structure,  their  chemical 
composition,  and  their  mode  of  existence. 

32.  The   distinctive  characteristic  of  inorganic  bodies  is 
•est ;  the  distinctive  trait  of  organized  bodies  is  independent 

motion,  LIFE.  The  rock  or  the  crystal,  once  formed,  nevei 
changes  from  internal  causes  ;  its  constituent  parts  or  mole- 
cules invariably  preserve  the  position  which  they  have  once 
taken  in  respect  to  each  other.  Organized  bodies,  on  the 
contrary,  are  continually  in  act '.on.  The  sap  circulates  in 


36          ELEMENTARY    STRUCTURE    OF    ORGANIZED    BODIES*. 

the  tree,  the  blood  flows  through  the  animal,  and  in  both 
there  is,  besides,  the  incessant  movement  of  growth,  decom 
position,  and  renovation. 

33.  Their  mode   of  formation   is  also  entirely  different. 
Unorganized  bodies  are  either  simple  or  made  up  of  ele- 
ments   unlike    themselves ;    and    when    a    mineral     is    en- 
larged, it  is  simply  by  the   outward  addition    of    particles 
constituted   like   Itself.      Organized   bodies  are   not  formed 
in  this  manner.     They  always,  and  necessarily,  are  derived 
from  beings  similar  to  themselves  ;  and  once   formed,  they 
always  increase  interstitially,  by  the  successive  assimilation 
of  new  particles,  derived  from  various  sources. 

34.  Finally,  organized  bodies  are  limited  in  their  duration. 
Animals  and  plants  are  constantly  losing  some  of  their  parts 
by  decomposition   during  life,  which  at  length  cease  to  be 
supplied,  and   they  die,  after  having  lived  for  a  longer  or 
shorter  period.     Inorganic   bodies,  on  the  contrary,  contain 
within   themselves   no   principle   of  destruction ;  and  unless 
subjected  to  some  foreign  influence,  a  crystal  or  a  rock  would 
never  change.     The  limestone  and  granite  of  our  mountains 
remain  just    as    they    were    formed    in   ancient   geological 
epochs ;  while  numberless  generations  of  plants  and   ani- 
mals have  lived  and  perished  upon  their  surface. 


SECTION  II. 

ELEMENTARY    STRUCTURE    OF    ORGANIZED   BODIES. 

35.  The  exercise  of  the  functions  of  life,  which  is  the 
essential  characteristic  of  organized  bodies,  (32,)  requires  a 
degree  of  flexibility  of  the  organs.  This  is  secured  by 
means  of  a  certain  quantity  of  watery  fluid,  which  pene 


ELEMENTARY    STRUCTURE    OF    ORGANIZED    BODIES          37 

trates  all  parts  of  the  body,  and  forms  one  of  its  principal 
constituents. 

36.  All  living  bodies,  without  exception,  are  made  up  of 
tissues  so  constructed  as  to  be  permeable  to  liquids.     There 
is  no  part  of  the  body,  no  organ,  however  hard  and  compact 
it  may  appear,  which  has  not  this  peculiar  structure.     It  ex- 
ists in  the  bones  of  animals,  as  well  as  in  their  flesh  and  fat ; 
tn  the  wood,  however  solid,  as  well  as  in  the  bark  and  flowers 
of  plants.     It  is  to  this  general  structure  that  the  terrr    or- 
ganism is   now  applied.     Hence   the    collective    name   of 
organized  beings,*  which  includes  both  the  animal  and  the 
vegetable  kingdoms. 

37.  The  vegetable  tissues  and  most  of  the  organic  struc- 
tures, when  examined  by  the  microscope 

in  their  early  states  of  growth,  are  found 
to  be  composed  of  hollow  vesicles  or  cells. 
The  natural  form  of  the  cells  is  that  of  a 
sphere  or  of  an  ellipsoid,  as  may  be  easily 
seen  in  many  plants ;  for  example,  in  the 
tissue  of  the  house-leek,  (Fig.  1.)  The  & 
intervals  which  sometimes  separate  them  Fig.  1. 

from  each  other  are  called  intercellular  passages  or  spaces 
(m.)  When  the  cellules  are  very  numerous,  and  crowd 
each  other,  their  outlines  become  angular,  and  the  intercel- 
lular spaces  disappear,  as  seen  in  figure  2,  which  represents 


*  Formerly,  animals  and  plants  were  said  to  ^organized,  because  they 
are  furnished  with  definite  parts,  called  organs,  which  execute  particular 
functions.  Thus,  animals  nave  a  stomach,  a  heart,  lungs,  &e  ;  plants 
have  leaves,  petals,  stamens  pistils,  roots,  &c.?  which  are  indispensable 
to  the  maintenance  of  life  and  the  perpetuation  of  the  species.  Sinco 
the  discovery  of  the  fundamental  identity  of  structure  of  animal  and 
vegetable  tissues,  a  common  denomination  for  this  uniformity  of  textuie 
has  been  justly  preferred;  and  the  existence  of  tissues  is  now  regarded 
as  the  basis  of  organization. 

4 


38         ELEMENTARY    STRUCTURE    OF    ORGANIZED    BODIES 

the  pith  of  the  elder.  They  then 
have  the  form  of  a  honey-comb ; 
whence  they  have  derived  their 
name  of  cellules. 

38.  All  the  organic  tissues,  whether 
animal  or  vegetable,  originate   from 

cells.      The   cell    is   to    the    organ-  Fig.  2. 

ized  body  what  the   primary  form  of  the  crystal  is  to  the 
secondary,  in  minerals.     As  a  general  fact,  it  may  be  stated 
6        that  animal  cells    are  smaller  than  vegetable 
—p.      jsi      cells ;  but  they  alike  contain  a  central  dot  or 
vg)     (jjj)     vesicle,  called  nucleus.     Hence  such  cells  are 
called  nucleated  cells,  (Fig.  3,  a.)     Sometimes 
the    nucleus    itself   contains    a    still    smaller 
dot,  called  nucleolus,  (b.) 

39.  The  elementary  structure  of  vegetables  may  be  ob 
served   in  every  part  of  a  plant,  and  its  cellular  character 
has  been  long  known.     But  with  the  animal  tissues  there  is 
far  greater  difficulty.     Their  variations  are  so  great,  and 
their  transformations  so  diverse,  that  after  the   embryonic 
period  it  is  sometimes  impossible,  even  by  the  closest  exam 
ination,  to  detect  their  original  cellular  structure. 

40.  Several  kinds  of  tissues  have  been  designated  in  the 
animal  structure  ;    but  their  differences  are  not  always  well 
marked,  and  they  pass  into  each  other  by  insensible  shades. 
Their  modifications  are  still  the  subject  of  investigation,  and 
we  refer  only  to  the  most  important  distinctions. 

41.  The  areolar  tissue  consists  of  a  network  of  delicate 
fibres,    intricately   interwoven    so   as  to   leave    numberless 
communicating   interstices,   filled    with  fluid.      It    is   inter- 
posed in  layers  of  various  thickness,  between  all  parts  of 
the  body,  and  frequently  accompanied   by  clusters   of  fat 
cells.     The  fiUvous  and   the  serous  membranes  are    mere 
modifications  of  this  tissue. 

42    The  cartilaginous  tissue  is  composed  of  nucleated 


ELEMENTARY    STRUCTURE    OF    dlGANIZED    BODIES. 


39 


Fig-  4. 


Fig.  5. 


cells,  the  intercellular  spaces  being  filled  with  a  more  com 
pact  substance,  called  the  hyaline  matter.     Figure  4  repre- 
sents a  slip  of  cartilage  from  the  horse,  under 
a  magnifying  power  of  one  hundred  and  twen- 
ty diameters. 

43.  The  osseous  or  bony  tissue  differs  from 
the  cartilaginous  tissue,  in  having  its  meshes 
filled  with  salts  of  lime,  instead  of  hyaline  sub- 
stance, whence  its  compact  and  solid  appear- 
ance.    It  contains,  besides,  minute,  rounded, 
or  star-like  points,   improperly   called   bone- 
corpuscles,  which  are  found  to  be  cavities  or 
canals,  sometimes   radiated  and  branched,  as 
is  seen  in  figure  5,  representing  a  section  of  a 
bone  of  a  horse,  magnified  four  hundred  times. 

44.  The  muscular  tissue,  which  forms  the    flesh  of  ani- 
mals, is  composed  of  bundles  of  parallel  fibres,  which  pos- 
sess the  peculiar  property  of  contracting  or  shortening  them- 
selves, under  the  influence  of  the  nerves.      In  the  muscles 
under   the   control   of  the    will,  the   fibres  are  commonly 
crossed   by  very  fine  lines  or  wrinkles  ;  but  not  so  in  the 
involuntary  muscles.     Every  one  is  sufficiently  familiar  with 
this  tissue,  in  the  form  of  lean  meat. 

45.  The   nervous   tissue  is   of  different   kinds.     In 

nerves  proper,  it  is  composed  of 

very  delicate  fibres,  which  return 

back    at   their   extremities,    and 

form  loops,  as  shown  in  figure  6, 

representing  nervous  threads   as 

they  terminate  in  the  skin  of  a 

frog.    The  same  fibrous  structure 

is  found  in  the  white  portion  of  the  brain. 

the  gray  substance  of  the  brain  is  composed  of 
vory  minute  granulations,  interspersed  with  clusters  of  larger 
cells,  as  seen  in  figure  7. 


the 


Fig.  7. 


Fig.  6. 


But 


40          ELEMENTARY    STRUCTURE    OF    OKj.,NIZED    BODIES. 

46.  The  tissues  above  enumerated  differ  from  each  othei 
more  widely,  in  proportion  as  they  are  examined  in  animals 
of  a  higher  rank.     As  we  descend  in  the  scale  of  being, 
the  differences  become  gradually  effaced.     The  soft  body 
of  a  snail   is  much   more   uniform  in  its  composition  than 
the  body   of  a  bird  or  a   quadruped.      Indeed,   multitudes 
of  animals  are  known  to  be  made  up  of  nothing  but  cells 
in  contact  with  each   other.      Such  is  the  case    with    the 
polyps;    yet   they   contract,   secrete,    absorb,    and    repro- 
duce; and  most  of  the  Infusoria  move   freely,  by  means  of 
little  fringes  on   their  surface,  arising  from  a  peculiar  kind 
of  cells. 

47.  A  no  less  remarkable  uniformity  of  structure  is  to  be 
observed  in  the  higher  animals,  in  the  earlier  periods   of 
their  existence,  before  the  body  has  Arrived  at  its  definite 
form.     The   head   of  the  adult  salr=on,  for  instance,   con- 
tains not  only    all  the  tissues  we  have   mentioned,  namely, 

bone,  cartilage,  muscle,  nerve,  brain, 
and  membranes,  but  also  bloodves- 
sels, glands,  pigments,  &c.  Let 
us,  however,  examine  it  during  the 
embryonic  state,  while  it  is  yet  in 
Fig.  8.  the  egg,  and  we  find  that  the  whole 

head  is  made  up  of  cells  which  differ  merely  in  their  dimen- 
sions ;  those  at  the  top  of  the  head  being  very  small,  those  sur- 
rounding the  eye  a  little  larger,  and  those  beneath  being  still 
larger,  (Fig.  8.)  It  is  only  at  a  later  period,  after  still  further 
development,  that  these  cellules  become  transformed,  some 
of  them  into  bone,  others  into  blood,  others  into  flesh,  &c. 

48.  Again  :   the  growth  of  the  body,  the  introduction  of 
various  tissues,  the  change  of  form  and  structure,  proceed  in 
such  a  manner  as  to  give  rise  to  several  cavities,  variously 
combined  among  themselves,  and  each  containing,  at  the 
end  of  these  transformations,  peculiar  organs,  or  peculiar 
systems  of  organs. 


DIFFERENCES    BETWEEN    ANIMALS    AND    PLANTS  41 

SECTION  III. 

DIFFERENCES    BETWEEN    ANIMALS    AND    PLANTS. 

49.  At   first  glance,   nothing  would   seem  more   widely 
different  than  animals  and  plants.     What  is  there  in  coin- 
mon,  for  instance,  between  an  oak  or  an  elm,  and  the  bird 
which  seeks  shelter  amid  their  foliage  ? 

50.  The   differences  are   usually   so    obvious,   that   this 
question  would  be  superfluous  if  applied  only  to  the  higher 
forms  of  the  two  kingdoms.     But  this  contrast  diminishes, 
in   proportion    as   their  structure   is  simplified ;  and   as  we 
descend   to   the   lower  forms,   the    distinctions  are  so  few 
and  so  feebly  characterized,  that  it  becomes  at  length  dif- 
ficult to  pronounce  whether  the  object  we  have  before  us  is 
an  animal  or  a  plant.     Thus,  the  sponges  have  so  great  a 
resemblance  to  some  of  the  polypi,  that  they  have  generally 
been  classed  among  animals,  although  in  reality  they   be 
long  to  the  vegetable  kingdom. 

51.  Animals  and   plants  differ  in  the    relative    predomi- 
nance of  the  elements,  oxygen,  carbon,  hydrogen  and  nitro- 
gen, of  which  they  are  composed.     In  vegetables,  only  a 
small  proportion  of  nitrogen  is  found  ;  while  it  enters  largely 
into  the  composition  of  the  animal  tissues. 

52.  Another  peculiarity  of  the  Animal  Kingdom  is,  the 
presence  of  large,  distinctly  limited  cavities,  usually  intended 
for  the  lodgment   of  certain  organs  ;  such  is  the  skull  and 
the  chest  in  the  higher  animals,  the  cavity  of  the  gills  in 
fishes,  and  of  the  abdomen,  or  general  cavity  of  the  body 
which  exists  in  all  animals,  without  exception,  for  the  pur- 
pose of  digestion,  or  the  reception  of  the  digestive  organs. 

53.  The  well-defined  and  compact  forms  of  the  organs 

4» 


42    '       DIFFERENCES    BETWEEN    ANIMALS    AND    FLINTS. 

lodge*,  in  these  cavities,  is  a  peculiarity  belonging  to  animals 
only.  I&  plants,  the  organs  designed  for  special  purposes 
are  never  embodied  into  one  mass,  but  are  distributed  over 
various  parts  of  the  individual.  Thus,  the  leaves,  which 
answer  to  the  lungs,  instead  of  being  condensed  into  one 
organ,  are  scattered  independently  in  countless  numbers  over 
the  branches.  Nor  is  there  any  organ  corresponding  to  the 
brain,  the  heart,  the  liver,  or  the  stomach. 

54.  Moreover,  the  presence  of  a  proper  digestive  cavity 
involves  marked  differences  between  the  two  kingdoms,  in 
respect  to  alimentation  or  the  use  of  food.     In  plants,  the 
fluids  absorbed  by  the  roots  are  carried,  through  the  trunk 
and  al!  the  branches,  to  the  whole  plant,  before  they  arrive 
at  the  leaves,  where  they  are  to  be  digested.     In  animals, 
on  the  contrary,  the  food  is  at  once  received  into  the  diges- 
tive cavity,  where  it  is  elaborated  ;  and  it  is  only  after  it  has 
been  thus  dissolved  and  prepared,  that  it  is  introduced  into 
the  other  parts  of  the  body.     The  food  of  animals  consists 
of  organized  substances,  while  that  of  vegetables  is  derived 
from    inorganic   substances  ;    and    they  produce    albumen, 
sugar,  starch,  &c.,  while  animals  consume  them. 

55.  Plants  commence  their  development  from   a   single 
point,  the  seed,  and,  in  like  manner,  all  animals  are  devel- 
oped from  the  egg.     But  the  animal  germ  is  the  result  of 
successive  transformations  of  the  yolk,  while  nothing  similar 
takes  place  in  the  plant.     The  subsequent  development  of 
individuals  is  for  the  most  part  different  in  the  two  kingdoms. 
No  limit  is  usually  placed  to  the  increase  of  plants  ;  trees 
put  out  new  branches  and  new  roots  as  long  as  they  live. 
Animals,  on  the  contrary,  generally  have  a  limited  size  and 
figure  ;  and  these  once  attained,  the  subsequent  changes  are 
accomplished  without  any  increase  of  volume,  or  essential 
alteration  of  form  ;  while  the  appearance  of  most  vegetables 
is  repeatedly  modified,  in  a  notable  manner,  by  the  develop- 


DIFFERENCES    BETWEEN    ANIMALS    AND    PLANTS.  43 

ment  of  new  branches.  Some  of  the  lowest  animals,  how- 
ever, the  polyps  for  instance,  increase  in  a  somewhat  analo- 
gous manner,  (§  329,  330.) 

56.  In  the  effects  they  produce  upon  the  air  by  respira- 
tion, there  is   an  important   difference.     Animals  consume 
the  oxygen,  and  give  out  carbonic  acid  gas,  which  is  de- 
structive to  animal  life  ;  while  plants,  by  respiration,  which 
they  in    most  instances  perform  by  means  of    the  leaves, 
reverse  the  process,  and  thus  furnish  oxygen,  which  is  so 
essential  to  animals.     If  an  animal  be  confined  in  a  small 
portion  of  air,  or  water  containing  air,  this  soon  becomes  so 
vitiated  by  respiration,  as  to  be  unfit  to  sustain  life;  but  if 
living  plants  are  enclosed  with  the  animal  at  the  same  time, 
the  air  is  maintained  pure,  and  no  difficulty  is  experienced. 
The  practical  effect  of  this  compensation,  in  the  economy  of 
Nature,  is  obviously  most  important ;   vegetation  restoring 
to  the  atmosphere  what  is  consumed  by  animal  respiration, 
combustion,  &c.,  and  vice  versa. 

57.  But  there  are  two  things  which,  more  than  all  others, 
distinguish  the  animal  from  the  plant,  namely,  the  power  of 
moving  itself  or  its  parts  at  will,  and  the  power  of  perceiv- 
ing other  objects  or  their  influences ;  in  other  words,  volun- 
tary motion  and  sensation. 

58.  All  animals  are   susceptible  of  undergoing  pleasure 
and  pain.     Plants  have   also   a   certain   sensibility.     They 
wither  and  fade  under  a  burning  sun,  or  when  deprived  of 
moisture ;  and  they  die  when  subjected  to  too  great  a  de- 
gree of  cold,  or  to  the  action  of  poisons      But  they  have  no 
consciousness  of  these  influences,  and  suffer  no  pain ;  while 
animals  under  similar  circumstances  suffer.      Hence   they 
have  been  called  animate    beings,  in  opposition  to  plants 
which  are  inanimate  oeings. 


J 


CHAPTER   THIRD. 

FUNCTIONS  AND  ORGANS  OF  ANIMAL  LIFE, 
SECTION  L 

OF  THE  NERVOUS  SYSTEM  AND  GENERAL  SENSATION. 

59.  LIFE,  in  animals,  is  manifested  by  two  sorts  of  func- 
tions, viz. :   First,  the  peculiar  functions  of  animcd  life,  or 
those  of  relation,  which  include  the  functions  of  sensation 
and  voluntary  motion  ;  those  which  enable  us  to  approach, 
and  perceive  our  fellow  beings  and  the  objects  about  us,  and 
to  bring  us  into  relation  with  them  :  Second,  the  functions 
of  vegetative  life,  which  are  nutrition  in  its  widest  sense, 
and  reproduction  ;  *  those  indeed  which  are  essential  to  the 
maintenance  and  perpetuation  of  life. 

60.  The    two   distinguishing   characteristics   of  animals, 
namely,  sensation  and  motion,   (57,)  depend  upon  special 
systems  of  organs,  which  are  wanting  in  plants,  the  nervous 
system  and  the  muscular  system  under  its  influence.     The 
nervous  system,  therefore,  is  the  grand  characteristic  of  the 
animal  body.     It  is  the  centre  from  which  all  the  commands 
of  the  will  issue,  and  to  which  all  sensations  tend. 


*  This  distinction  is  the  more  important,  inasmuch  as  the  organs  of 
animal  life,  and  those  of  vegetative  life,  spring  from  very  distinct  layers 
of  the  embryonic  membrane.  The  first  are  developed  from  the  uppe. 
.layer,  and  the  second  from  the  lower  layer  of  the  germ  of  the  animal 
See  Chapter  on  Embryology,  p.  112. 


NKRVOUS  SYSTEM  AND  GENERAL  SENSATION.      45 

61.  Greatly  as  the  form,  the  arrangement,  and  the  volj 
ame    of  the   nervous  system 

vary  in  different  animals, 
they  may  all  be  reduced  to 
four  principal  types,  which 
correspond,  moreover,  to  the 
four  great  departments  of  the 
Animal  Kingdom.  In  the 
vertebrate  animals,  namely, 
the  fishes,  reptiles,  birds,  and 
mammals,  the  nervous  sys- 
tem is  composed  of  two  prin- 
cipal masses,  the  spinal  mar- 
row, (Fig.  9,  c,)  which  runs 
along  the  back,  and  the 
brain,  contained  within  the 
skull.*  The  volume  of  the 
brain  is  proportionally  larger 
as  the  animal  occupies  a 
more  elevated  rank  in  the 
scale  of  being.  Man,  who 
stands  at  the  head  of  Crea- 
tion, is  in  this  respect  also  the 
most  highly  endowed  being.  Fig- 

62.  With  the  brain  and  spinal  marrow  are  connected  tho 
nerves,    which    are    distributed,    in    the  form  of   branching 
threads,    through   every  part  of  the    body.     The   branches 
which  unite  with  the  brain  are  twelve  pairs,  called    ihe  cere- 


*  The  brain  is  composed  of  several  distinct  parts  which  vary  greatly,  in 
their  relative  proportions,  in  different  animals,  as  will  appear  hereafter 
They  are  —  1.  The  medulla  oblongata ;  2.  Cerebellum;  3.  Optic  lobes; 
4.  Cerebral  hemispheres;  5.  Olfactory  lobes;  6.  the  pituitary  body ;  7 
the  pineal  body.  (See  figures  9  and  21.)  The  spinal  marrow  is  made  up 
by  the  union  of  four  nervous  columns 


46  NERVOUS    SYSTEM    AND   GENERAL    SENSATION. 

bral  nerves,  and  are  designed  chiefly  for  the  organs  of 
sense  located  in  the  head.  Those  which  join  the  spinal 
marrow  are  also  in  pairs,  one  pair  for  each  vertebra  or 
joint  of  the  back.  The  number  of  pairs  varies,  therefore,  in 
different  classes  and  families,  according  to  the  number  of 
vertebrae.  Each  nerve  is  double,  in  fact,  being  composed 
of  two  threads,  which  at  their  junction  with  the  spinal  mar- 
row are  separate,  and  afterwards  accompany  each  other 
throughout  their  whole  course.  The  anterior  thread  trans 
mits  the  commands  of  the  will  which  induce  motion ;  the 
other  receives  and  conveys  impressions  to  the  brain,  to  pro- 
duce  sensations. 

63.  In   the   Articulated   animals,  comprising   the   crabs, 

barnacles,  worms,  spi- 
ders, insects,  and  oth- 
er animals  formed  of 
rings,  the  nervous  sys- 

Fig.  10.  tern  consists  of  a  se- 

ries of  small  centres  or  swellings,  called  ganglions,  (Fig.  10,) 
placed  beneath  the  alimentary  canal,  on  the  floor  of  the  gen- 
eral cavity  of  the  body,  and  connected  by  threads  ;  and  of  a 
more  considerable  mass  placed  above  the  oesophagus  or 
throat,  connected  with  the  lower  ganglions  by  threads  which 
form  a  collar  around  the  alimentary  canal.  The  number  of 
ganglions  generally  corresponds  to  the  number  of  rings. 

64.  In  the  Mollusks,  (Fig.  11,)  the  nervous  system  con- 

sists of  a  single  gangl  ionic 
circle,  the  principal  swell- 
ings of  which  are  placed 
symmetrically  above  and 
below  the  oesophagus,  and 
from  whence  the  filaments, 
Fig.  11.  which  supply  the  organs 

in  different  directions,  take  their  origin. 


NERVOUS    SYSTEM    AND    GENERAL    SENSATION.  47 

65.  In  the  Radiata,  (Fig.  12,)  the  nervous  system  is  re- 
duced to  a  single  ring,  encircling 

the  mouth,  and  giving  off  .threads 
towards  the  circumference.  It  dif- 
fers essentially  from  that  of  the 
Mollusks,  by  being  disposed  in  a 
horizontal  position,  and  by  its  star- 
like  form. 

66.  The  nerves  branch  off  and 
diffuse  sensioility  to  every  portion 

of  the  body,  and  thereby  men  and  Fig- 12- 

the  higher  animals  are  enabled  to  gain  a  knowledge  of  the 
general  properties  of  the  objects  which  surround  them ;  every 
point  of  the  body  being  made  capable  of  determining  whether 
an  object  is  hot  or  cold,  dry  or  moist,  hard  or  soft,  &c.  There 
are  some  parts,  however,  the  ends  of  the  fingers,  for  exam- 
ple, in  which  this  sensibility  is  especially  acute,  and  these 
also  receive  a  larger  supply  of  nerves. 

67.  On  the  contrary,  those  parts  which  are  destitute  of 
sensibility,  such  as  the  feathers  of  birds,  the  wool  of  ini- 
mals,  or  the  hair  of  man,  are  likewise  destitute  of  nerves. 
But  the  conclusive  proof  that  sensibility  resides  in  the  nerves 
is,  that  when  the  nerve  which  supplies  any  member  of  the 
body  is  severed,  that  member  at  once  becomes  insensible. 

68.  There  are  animals  in  which  the  faculty  of  percep- 
tion is  limited  to  this  general   sense ;    but   their  number  is 
small,  and,  in  general,  they  occupy  the  lowest  place  in  the 
series.     Most  animals,  in  addition  to-  the  general  sensibility, 
are  endowed  with  peculiar  organs  /or  certain  kinds  of  per- 
ceptions, which  are  acted  upon  by  certain  kinds  of  stimuli, 
as  light,  sound  and  odor,  and  which  are  called  the  SENSES. 
These  are  five  in  number,  namely :    sight,  hewing, 
taste,  and 


-f- 


<18  SPECIAL    SENSES 

SECTION  II. 

OF    THE    SPECIAL    SENSES. 

1.     Of  Sight. 

69.  Sight  is  the  sense  by  which  light  is  perceived,  and 
by  means  of  which  the  outlines,  dimensions,  relative  posi- 
tion, color  and  brilliancy  of  objects  are  discerned.     Some 
of  these  properties  may  be  also  ascertained,  though  in  a  less 
perfect  manner,  by  the  sense  of  touch.     We  may  obtain  an 
idea  of  the  size  and  shape  of  an  object,  by  handling  it ;  but 
the  properties  that  have  a  relation  to  light,  such  as  color  and 
brilliancy,  and  also  the  form  and  size  of  bodies  that  are  be- 
yond our  reach,  can  be  recognized  by  sight  only. 

70.  The  EYE  is  the  organ  of  vision.     The  number,  struc- 
ture, and  position  of  the  eyes  in  the  body  is  considerably 
varied  in  the  different  classes.     But  whatever  may  be  their 
position,  these  organs  in  all  the  higher  animals  are  in  connec- 
tion with  particular  nerves,  called  the  optic  nerves,  (Fig.  13, 
a.)     In  the  vertebrates,  these  are  the  second  pair  of  the  cer- 
ebral nerves,  and  arise  directly  from  the  middle  mass  of  the 
brain,  (Fig.  21,  Z>,)  which,  in  the  embryo,  is  the  most  con- 
siderable of  all. 

71.  Throughout  the  whole  series  of  vertebrate  animals 

the  eyes  are  only  two  in  num- 
ber, and  occupy  bony  cavities 
of  the  skull,  called  the  orbits. 
The  organ  is  a  globe  or  hollow 
sphere  formed  by  three  princi- 
pal membranes,  enclosed  one 
within  the  other,  and  filled  with 
transparent  matter.  Figure  13 
represents  a  vertical  section 


OF    SIGHT.  49 

through  the  eye,  from  before  backwards,  and  will  give  an 
idea  of  the  relative  position  of  these  different  parts. 

72.  The  outer  coat  is  called  the  sclerotic,  (b ;)   it  is  a 
thick,  firm,   white    membrane,  having   its   anterior   portion 
transparent.     Th^s  transparent  segment,  which  seems  set  in 
the  opaque  portion,  like  a  watch-glass  in  its  rim^is  called  the 
cornea,  (f.) 

73.  The  inside  of  the  sclerotic  is  lined  by  a  thin,  dark- 
colored  membrane,  the  choroid,  (c.)     It  becomes  detached 
from  the  sclerotic  when  it  reaches  the  edge  of  the  cornea, 
and  forms  a  curtain  behind  it.     This  curtain  gives  to  the  eye 
its  peculiar  color,  and  is  called  the  iris,  (g.)     The  iris  read- 
ily contracts  and  dilates,  so  as  to  enlarge  or  diminish  an  open- 
ing at  its  centre,  the  pupil,  according  as  more  or  less  light 
is  desired.     Sometimes  the  pupil  is  circular,  as  in  man,  the 
dog,  the  monkey;  sometimes  in  the  form  of  a  vertical  ellipse, 
as  in  the  cat ;  or  it  is  elongated  sidewise,  as  in  the  sheep. 

74.  The  third  membrane  is  the  retina,  (d.)     It  is  formed 
by  the  optic  nerve,  which  enters  the  back  part  of  ihe  eye,  by 
an  opening  through  both  the  sclerotic  and  choroid  coats,  and 
expands  upon  the  interior  into  a  whitish  and  most  delicate 
membrane.     It  is  upon  the  retina  that  the  images  of  objects 
are  received,  and  produce  impressions,  which  are  conveyed 
by  the  nerve  to  the  brain. 

75.  The  fluids  which  occupy  the  cavity  of  the  eye  are  of 
different  densities.    Behind,  and  directly  opposite  to  the  pupil, 
is  placed  a  spheroidal  body,  called  the  crystalline  lens,  (c.) 
It  is  tolerably  firm,  perfectly  transparent,  and  composed  of 
layers  of  unequal  density,  the   interior  being  always  more 
compact  than  the  exterior.     Its  form  varies  in  different  classes 
of  animals.     In  general,  it  is  more  convex  in  aquatic  than  in 
land  animals;  whilst  with  the  cornea  it  is  directly  the  con- 
trary, being  flat  in  the  former,  and  convex  in  ihe  latter. 

76.  By  means  of  the  iris,  the  cavity,  (i,)  in  front  of  the  crys- 

5 


50  SPECIAL    SENSES. 

talline  lens  is  divided  into  two  compartments,  called  .he  an 
terior  and  posterior  chambers.  The  fluid  which  fi  is  tnese 
chambers  is  a  clear  watery  liquid,  called  the  aqueous  humor 
The  portion  of  the  globe  behind  the  lens,  which  is  much  the 
largest,  is  filled  by  a  gelatinous  liquid,  perfectly  transparent, 
'like  that  of  the  chambers,  but  somewhat  more  dense.  Tnis 
is  called  the  vitreous  humor,  (h.) 

77.  The  object  of  this  apparatus  is  to  receive  the  rays  of 
light,  which  diverge  from  all  points  of  bodies  placed  before 
it,  and  to  bring  them  again  to  a  point  upon  the  retina.  It  is 
a  well-known  fact,  that  when  a  ray  of  light  passes  obliquely 
from  one  medium  to  another  of  different  density,  it  will  be 
refracted  or  turned  out  of  its  course  more  o-  loss,  according 
to  the  difference  of  this  density,  and  the  obliquity  at  which 
the  ray  strikes  the  surface.  This  may  be  illustrated  by  the 
following  figure,  (Fig.  14.) 


Fig.  14. 

The  ray  a  c,  which  strikes  the  cornea  A  B  perpendicularly, 
continues  without  deviation,  until  it  reaches  the  bottom  ot 
the  eye  at  c.  But  the  rays  a  m  and  a  n,  which  strike  the  eye 
obliquely,  change  their  direction,  and  instead  of  proceeding 
onward  to  m  g  and  n  d,  take  the  direction  m  i  and  n  f  A 
still  further  refraction,  though  less  considerable,  is  occasioned 
by  passing  through  the  crystalline  lens  C  D,  and  the  vitreous 
humor,  so  that  the  two  rays,  m  i  and  nf,  will  at  last  meet  in 
?jt  point.  This  point  is  called  the  focus,  (c,)  and  in  distinc 
vision  \s  always  precisely  at  the  retina,  E  F. 

78.    From   this  arrangement,   the  image  found  upon  the 


OF    SIGHT.  51 

retina  will  be  inverted.  We  may  satis.fy  ourselves  c  f  this 
by  direct  observation.  The  eye  of  the  white  rabbit  being 
destitute  of  the  black  pigment  of  the  choroid,  is  quite  trans- 
parent. Take  the  eye,  soon  after  the  death  of  the  animal, 
and  arrange  it  in  one  end  of  a  tube,  so  that  the  cornea  will 
face  outwards ;  then  if  we  look  in  at  the  other  end  of 
the  tube,  we  may  see  objects  to  which  it  is  directed  exactly 
pictured  upon  the  retina,  but  in  a  reversed  position. 

79.  The   mechanical  structure  of  the  eye   may  be  per- 
fectly imitated  by  art.     Indeed,  the  camera  obscura  is  an 
instrument  constructed  on  the  very  same  plan.     By  it,  exter- 
nal objects  are  pictured  upon  a  screen,  placed  at  the  bottom 
of  the  instrument,  behind  a  magnifying  lens.     The  screen 
represents  the  retina ;   the    dark  walls  of  the    instrument 
represent  the  choroid  ;  and  the  cornea,  the  crystalline  lens 
and  the  vitreous  humor  combined,  are, represented   by  the 
magnifying  lens.     But  there  is  this  important  difference,  that 
the  eye  has  the  power  of  changing  its  form,  and  of  adapt- 
ing itself  so  as  to  discern  with  equal  precision  very  remote, 
as  well  as  very  near,  objects. 

80.  By  means  of  muscles  which  are  attached  to  the  bali, 
the  eyes  may  be  rolled  in  every  direction,  so  as  to  view  ob- 
jects on  all  sides,  without  moving  the  head.     The  eyes  are 
usually  protected  by  lids,  which  are  two  in  the  mammals, 
and  generally  furnished  with  a  range  of  hairs  at  their  edges, 
called  eye-lashes.     Birds  have  a  third  lid,  which  is  vertical ; 
this  is  also  found  in  most  of  the  reptiles  and  a  few  man.- 
mals.     In  fishes,  the  lids  are  wanting,  or  immovable. 

81.  The  eye  constructed  as  above  described  is  called  a 
simple  eye,  and  belongs  more   especially  to  the  vertebrate 
animals.     In  man,  it  arrives  at  its  highest  perfection.     In 
him,  the  eye  also  performs  a  more  exalted  office  Uan  mere 
vision.     It  is  a  mirror,  in  which  the  inner  man  is  reflected. 
His  passions,  his  joys,  and  his  sorrows,  his  inmost  self,  are 


52  SPECIAL    SENSES. 

revealed,  with  the  utmost  fidelity,  in  the  expression  of  his 
eye,  and  it  has  been  rightly  called  "  the  window  of  the 
soul." 

82.  Many  of  the    invertebrate    animals    have   the    eye 
constructed  upon  the  same  plan  -as  that  of  the  vertebrate 
animals,   but  with  this  essential  difference,  that  the  optic 
nerve  which  forms  the   retina  is  not  derived  from  a  ner- 
vous centre,  analogous  to  the  brain,  but  arises  from  one 
of  the  ganglions.     Thus,  the  eye  of  the  cuttle-fish  contains 
all  the  essential  parts  of  the  eye  of  the  superior  animals, 
and,  what  is  no  less  important,  they  are  only  two  in  number, 
placed  upon  the  sides  of  the  head. 

83.  The  snail  and  kindred  animals  have,  in  like  manner, 

only  two  eyes,  mounted  on  the  tip 
of  a  long  stalk,  (the  tentacle,)  or 
situated  at  its  base,  or  on  a  short 

,  ^s  pedestal   by  its   side.      Their   struc- 

" — -~^Xb  ture  is  less  perfect  than  in  the  cuttle- 

Fig.  15.  fish,  but  still  there  is  a  crystalline  lens, 

and  more  or  less  distinct  traces  of  the  vitreous  body.  Some 
bivalve  mollusks,  the  scollops  for  example,  have  likewise 
a  crystalline  lens,  but  instead  of  two  eyes,  they  are  furnished 
with  numerous  eye-spots,  which  are  arranged  like  a  border 
around  the  lower  margin  of  the  animal. 

84.  In  spiders,  the  eyes  are  likewise  simple,  and  usually 

eight  in  number.  These 
little  organs,  usually  called 
ocelli,  instead  of  being 
placed  on  the  sides  of 
the  body  or  of  the  head, 
occupy  the  anterior  part 
of  the  back.  All  the  essen- 
Fig.  16.  tial  parts  of  a  simple  eye 

the  corner ,  the  crystalline  lens,  the  vitreous  body,  are  found  in 


OF    SIGHT.  53 

hem,  and  even  the  choroid,  which  presents  itself  in  the 
form  of  a  black  ring  around  the  crystalline  lens.  Many  in 
sects,  in  their  caterpillar  state,  also  have  simple  eyes. 

85.  Rudiments   of    eyes  have    been   observed    in   very 
many  of    the    worms.     They,  generally    appear   as   small 
black  spots  on  the  head  ;    such  as  are   seen  on   the  head 
of  the  Leech,  the  Planaria  and  the  Nereis.     In  these  latter 
animals  there  are  four  spots.     According  to  Muller,  they 
are   small   bodies,  rounded  behind,  and   flattened   in   front, 
composed  of  a  black,  cup-shaped  membrane,  containing  a 
small  white,  opaque  body,  which  seems  to  be  a  continuation 
of  the  optic  nerve.     It  cannot  be   doubted,  therefore,  that 
these   are    eyes ;    but   as   they  lack  the    optical  apparatus 
which    produces   images,  we   must   suppose    that  they  can 
only  receive  a  general  impression  of  light,  without  the  power 
of  discerning  objects. 

86.  Eye-spots,  very    similar 
to    those    of    the    Nereis,   are 
found  at  the  extremity  of  the 
rays  of  some  of  the  star-fishes, 
in  the  sea-urchins,  at  the  mar- 
gin of  many  Medusae,  and    in 
some    Polypi.     Ehrenberg  has 
shown    that   similar   spots  also 
exist  in  a  large  number  of  the 

Infusoria.  Fig.  17. 

87.  In  all  the  above-mentioned  animals,  the  eyes,  what 
ever  their  number,  are  apart  from  each  other.     But  there  is 
still  another  type  of  simple  eyes,  known  as  aggregate  eyes. 
In  some  of  the  millipedes,  the  pill-bugs,  for  instance,  the  eyes 
are  collected  into  groups,  like  those  of  spiders;  each  eye 
inclosing  a  crystalline  lens  and  a  vitreous  body,  surrounded 
by  a  retina  and  choroid.    Such  eyes  consequently  form  a 


54 


SPECIAL    SENSES. 


natural  transition  to  the  compound  eyes  of  insects,  to  which 
we  now  give  our  attention. 

88.  Compound  eyes  have  the  same  general  form  as 
simple  eyes  ;  they  are  placed  either  on  the  sides  of  the  head, 
as  in  insects,  or  supported  on  pedestals,  as  in  the  crabs. 
But  if  we  examine  an  eye  of  this  kind  by  a  magnifying  lens, 
we  find  its  surface  to  be  composed  of  an  infinite  number  of 
angular,  usually  six-sided  faces.  If  these  fapettes  are  re- 
moved, we  find  beneath  a  corresponding  number  of  cones,  (c,) 
side  by  side,  five  or  six  times  as  long  as  they  are  broad, 
and  arranged  like  rays  around  the  optic  nerve,  from 
which  each  one  receives  a  little  filament,  so  as  to 
present,  according  to  Muller,  the  following  disposition. 

(Fig.  18.)  The  cones  are  per- 
fectly transparent,  but  sepa- 
rated from  each  other  by 
walls  of  pigment,  in  such  a 
manner  that  only  those  rays 
which  are  parallel  to  the 
axes  can  reach  the  retina  A ; 
all  those  which  enter  ob- 
liquely are  lost ;  so  that  of 
Fig. 18.  all  the  rays  which  proceed 

from  the  points  a  and  £,  only  the  central  ones  in  each 
pencil  will  act  upon  the  optic  nerve,  (d ;)  the  others  will 
strike  against  the  walls  of  the  cones.  To  compensate 
for  the  disadvantage  of  such  an  arrangement,  and  for  the 
want  of  motion,  the  number  of  fa£ettes  is  greatly  multi- 
plied, so  that  no  less  than  25,000  have  been  counted  in 
a  single  eye.  The  image  on  the  retina,  in  this  case,  may 
be  compared  to  a  mosaic,  composed  of  a  great  number  of 
small  image?  each  of  them  representing  a  portion  of  the 
figure.  Tht  entire  picture  is  of  course,  more  perfect, 


OF    HEARING.  55 

in    proportion    as    the  pieces    are  smaller  and   more    nu- 
merous. 

89  Compound  eyes  are  destitute  of  the  optical  apparatus 
necessary  to  concentrate  the  rays  of  light,  and  cannot  adapt 
themselves  to  the  distance  of  objects  ;  they  see  at  a  certain 
distance,  but  cannot  look  at  pleasure.  The  perfection  of 
their  sight  depends  on  the  number  of  fayettes  or  cones, 
and  the  manner  in  which  they  are  placed.  Their  field  of 
vision  is  wide,  when  the  eye  is  prominent;  it  is  very  limited, 
on  the  contrary,  when  the  eye  is  flat.  Thus  the  dragon-flies, 
on  account  of  the  great  prominency  of  their  eyes,  see  equally 
well  in  all  directions,  before,  behind,  or  laterally ;  whilst 
the  water-bugs,  which  have  the  eyes  nearly  on  a  level  with 
the  head,  can  see  to  only  a  very  short  distance  before  them. 

90.  If  there  be  animals  destitute  of  eyes,  they  are  either 
of  a  very  inferior  rank,  such  as  most  of  the  polypi,  or  else 
they   are    animals    which    live    under   unusual   circumstan- 
ces, such  as  the  intestinal  worms.     Even  among  the  ver- 
tebrates, there  are  some  that  lack  the   faculty   of  sight,  as 
the  Myxine  glutinosa,  which  has  merely  a  rudimentary  eye 
concealed  under  the  skin,  and  destitute  of  a  crystalline  lens. 
Others,  which  live  in  darkness,  have  not  even  rudimentary 
eyes,  as,  for  example,  that  curious  fish  (Amblyopsis  spelceus,) 
which  lives  in  the  Mammoth  Cave,  and  which  appears  to 
want   even  the  orbital  cavity.     The   craw-fishes,  (Astacus 
pellucidus,)    of    this   same   cave,  are   also   blind ;    having 
merely  the    pedicle    for    the    eyes,  without  any  traces  of 
fayettes. 

2.  Hearing. 

91,  To  hear,  is  to  perceive  sounds.     The  faculty  of  per- 
ceiving sounds  is  seated  in  a  peculiar  apparatus,  the  EAR, 
which  is  constructed  with  a  view  to  collect  and  augment  the 
sonorous  vibrations  of  the  atmosphere,  and  convey  them  to 


56  SPECIAL    SENSES. 

the  acoustic  or  auditory  nerve,  which  arises  from  the  poste- 
rior part  of  the  brain.     (Fig.  21,  c.) 

92.  The    ears  never  exceed   two  in  number,   and    are 
placed,  in  all  the  vertebrates,  at  the  hinder  part  of  the  head. 
In  a  large  proportion  of  animals,  as  the  dog,  horse,  rabbit, 
and  most  of  the   mammals,  the  external  parts   of  the   ear 
are   generally  quite  conspicuous  ;    and    as  they  are,  at  the 
same  time,  quite  movable,  they  become   one   of  the  promi- 
nent features  of  physiognomy. 

93.  These  external  appendages,  however,  do  not  const! 
tute  the  organ  of  hearing-,  properly  speaking.     The  true  seat 
of  hearing  is  deeper,  quite  in  the  interior  of  the  head.     It  is 
usually  a  very  complicated  apparatus,  especially  in  the  supe- 
rior animals.     In  mammals  it  is  composed  of  three  parts,  the 
external   ear,  the  middle  ear,  and  the  internal  ear ;   and  its 
structure  is  as  follows  :     (Fig.  19.) 


Fig.  19. 

94.  The  external  ear,  which  is  popularly  regarded  as  the 
rar,  consists  of  the  conch,  (#,)  and  the  canal  which  leads 
from  it  the  external  auditory  passage,  (&.)  The  first  is  a 


OF    HEARING  57 

gristly  expansion,  in  the  form  of  a  norn  or  a  funnel,  the 
object  of  which  is  to  collect  the  waves  of  sound  ;  for  this 
reasor. ,  animals  prick  up  their  ears  when  they  listen.  •  The 
ear  of  man  is  remarkable  for  being  nearly  immovable. 
Therefore,  persons,  whose  hearing  is  deficient,  employ  an 
artificial  trumpet,  by  which  the  vibrations  from  a  much 
more  extended  surface  may  be  collected.  The  external 
ear  is  peculiar  to  mammals,  and  is  wanting  even  in  some 
aquatic  species  of  these,  such  as  the  seals  and  the  Orni- 
thorhyncus. 

95.  The  middle  ear  has  received  the  najme  of  the  tym- 
panic cavity,  (k.)     It  is  separated  from  the  auditory  passage 
by  a  membranous   partition,  the  tympanum  or  drum,   (c ;) 
though  it  still  communicates  with  the  open  air  by  means 
of  a  narrow  canal,  called   the   Eustachian  tube,  (i,)   which 
opens  at  the  back  part  of  the  mouth. 

In  the  interior  of  the  chamber  are 
four  little  bones,  of  singular  forms, 
which  anatomists  have  distinguished 
by  the  names  of  malleus,  (Fig.  20,  c,) 
incus,  (n,)  stapes,  (s,)  and  os  orbicu- 
lare,  (o;)  which  are  articulated  to- 
gether, so  as  to  form  a  continuous 
chain,  as  here  represented,  magnified. 

96.  The   internal  ear,  which    is 

also  denominated  the  labyrinth,  is  an  irregular  cavity  formed 
in  the  most  solid  part  of  the  temporal  bone,  beyond  trie 
chamber  of  the  middle  ear,  from  which  it  is  separated  by  a 
bony  partition,  which  is  perforated  by  two  small  holes,  called, 
from  their  form,  the  round  and  the  oval  apertures,  the  fora- 
men rotundum,  (Fig.  19,  g,)  and  the  foramen  ovale,  (A.)  The 
first  is  closed  by  a  membrane,  similar  to  that  of  the  tympa- 
num, while  the  latter  is  closed  by  the  stapes,  one  of  the  little 
bones  n  the  chamber. 


58  SPECIAL    SENSES. 

97.  Three  parts  a:e  to  be  distinguished   in  the  labyrinth, 
namely,  the  vestibule,  which  is  the  part  at  the  entrance  of  the 
cavity ;   the  semicircular  canals,  (d,)  which  occupy  its  uppei 
part,  in  the  form   of  three   arched   tubes;  and  the  cochlea^ 
which  is  a  narrow  canal  placed  beneath,  at  the   lower  part 
of  the  vestibule,  having  exactly  the  form  of  a  snail-shell,  (e.) 
The  entire  labyrinth   is  filled  with  a  watery  fluid,  in  which 
membranous  sacs  or  pouches  float.     Within  these  sacs,  the 
auditory   nerve  (f)  terminates.     These  pouches,  therefore, 
are  the  actual  seat  of  hearing,  and  the  most  essential   parts 
of  the  ear.     The  auditory  nerve  is  admitted  to  them  by  a 
long  passage,  the  internal  auditory  canal. 

98.  By  this  mechanism,  the  vibrations  of  the  air  are  first 
collected   by  the  external  ear,  whence  they  are  conveyed 
along  the  auditory  passage,  at  the  bottom  of  which  is  the 
tympanum.     The  tympanum,  by  its  delicate  elasticity,  aug- 
ments the  vibrations,  and  transmits  them  to  the  internal  ear, 
partly  by  means  of  the  little  bones  in  the  chamber,  which  are 
disposed  in  such  a  manner  that  the  stapes  exactly  fits  the  oval 
aperture,  (foramen  ovale;)  and   partly  by  means  of  the  air 
which  strikes  the  membrane  covering  the  round  aperture,  (#•,) 
and  produces  vibrations  there,  corresponding  to  those  of  the 
tympanum.      After  all  these    modifications,    the    sonorous 
vibrations  at  last  arrive  at  the  labyrinth  and   the  auditory 
nerve,  which  transmits  the  impression  to  the  brain. 

99.  But  the  mechanism  of  hearing  is  not/so  complicated 
in  all  classes  of  animals,  and  is  found  to  be  more  and  more 
simplified   as  we   descend  the  series.     In  birds,  the  middle 
and  interior  ears  are  constructed  on  the  same  plans  as  in  the 
mammals ;  but  the  outer  ear  no  longer  exists,  and  the  audi- 
tory passage,  opening  on  a  level  with  the  surface  of  the  head 
behind  the  eyes,  is  merely  surrounded  by  a  circle  of  peculi- 
arly formed  feathers.     The  bones  of  the  middle  ear  are  also 
less  numerous  there  being  generally  but  one. 


OF    HEARING.  59 

100.  In  reptiles,  the  whole  exterior  ear  disappears ;  the 
auditory  passage  is  always  wanting,  and  the  tympanum  be- 
comes external.     In  some  toads,  even  the  middle  ear  also  is 
completely  wanting.     The  fluid  of  the  vestibule  is  charged 
with  salts  of  lime,  which  frequently  give  it  a  milky  appear- 
ance,  and   which,  when  examined  by  the  microscope,  are 
found  to  bo  composed  of  an  infinite  number  of  crystals. 

101.  In  fishes,  the    middle    and    external   ear   are  both 
wanting;  and  the  organ  of  hearing  is  reduced  to  a  mem- 
branous vestibule,  situated  in  the  cavity  of  the  skull,  and 
surmounted  by  semicircular  canals,   from   one  to  three  in 
numoer.     The  liquid  of  the  vestibule  contains  chalky  con- 
cretions of  irregular  forms,  which  are  called  Otolites,  the 
use  of  which  is  doubtless  to  render  the  vibration  of  sounds 
more  sensible. 

102.  In  crabs,  the  organ  of  hearing  is  found  on  the  lower 
face  of  the  head,  at  the  base  of  the  large  antennse.     It  is  a 
bony  chamber  closed  by  a  membrane,  in   the  interior  of 
which  is  suspended  a  membranous  sac  filled  with  water.     On 
this  sac,  the  auditory  nerve  is   expanded.     In  the  cuttlefish, 
the  vestibule  is  a  simple  excavation  of  the  cartilage  of  the 
head,  containing  a  little  membranous  sac,  in  which  the  audi- 
tory nerve  terminates. 

103.  Finally,  some  insects,  the  grasshopper  for  instance, 
have  an  auditory  apparatus,  no  longer  situated  in  the  head, 
as  with  other  animals,  but  in  the  legs  ;  and  from  this  fact,  we 
may  be  allowed  to  suppose,  that  if  no  organ  of  hearing  has 
yet  been  found  in   most  insects,  it  is  because  it  has  beeii 
sought  for  in  the  head  only.. 

104.  It  appears  from  these  examples,  that  the  part  of  the 
organ  of  hearing  which  is  uniformly  present  in  all  animals 
furnished  with  ears,  is  precisely  that  in  which  the  auditory 
nerve  ends.     This,  therefore,  is  the  essential  part  of  the  or- 
gan.    The    other   parts   of  the    apparatus,   the    tympanum, 
audit .iry  passage,  a- id  even  the  semicircular  canals,  have  for 


60 


SPECIAL    SENSES. 


their  object  merely  to  aid  the  perception  of  sound  with  more 
precision  and  accuracy.  Hence  we  may  conclude  that  the 
sense  of  hearing  is  dull  in  animals  where  the  organ  is  re- 
duced to  its  most  simple  form  ;  and  that  animals  which  have 
merely  a  simple  membranous  sac,  without  tympanum  an! 
auditory  passage,  as  the  fishes,  or  without  semicircular 
canals,  as  the  crabs,  perceive  sounds  in  but  a  very  imper- 
fect manner.  J/ 

3.     Of  Smell 

105.  SMELL    is  the  faculty  of   perceiving   odors,  and  is 

a  highly  important 
sense  to  many  ani- 
mals. Like  sight 
and  hearing,  smell 
depends  upon  special 
nerves,  the  olfacto- 
ry, (a,)  which  are 
the  first  pair  of  cer- 
p.  21  ebral  nerves,  and 

which,    in    the    em- 
a,  olfactory  nerve;  b,  optic  nerve;  c,  audi-         i  j- 

,  bivo,  are  direct  pro- 

tory  nerve ;    a,   cerebrum ;    e,   cerebellum ; 

/,  nostril.  longations     of     the 

brain. 

106.  The  organ  of  smell  is  the  NOSE.     Throughout  the 
series  of  vertebrates,  it  makes  a  part  of  the  face,  and  in 
man,  by  reason  of  its  prominent  form,  it  becomes  one  of  tne 
dominant  traits  of  his  countenance  ;  in  other  mammals,  the 
nose  loses  this  prominency  by  degrees,  and  the  nostrils  no 
longer  open  downwards,  but  forwards.     In  birds,  the  position 
of  the  nostrils  is  a  little  different ;  they  open  farther  back 
and  higher,  at  the  origin  of  the  beak,  (/.) 

107.  The  nostrils  are  usually  two  in  number.     Some  fishes 
have  four.     They  are  similar  openings,  separated  by  a  par- 
tition  upon  the  middle  line  of  the  body.     In  man  and  the 


OF    SMELL.  61 

mammals,  the  outer  walls  of  the  nose  are  composed  of  carti- 
lage ;  but  internally,  the  nostrils  communicate  with  bony  cav- 
ities situated  in  the  bones  of  the  face  and  forehead.  These 
cavities  are  lined  by  a  thick  membrane,  the  pituitary  mem 
biuue,  on  which  are  expanded  the  nerves  of  smell,  namely, 
the  olfactory  nerves,  and  some  filaments  of  the  nerve  which 
goes  to  the  face. 

108.  The  process  of  smelling  is  as  follows.     Odors  are 
particles  of  extreme  delicacy  which  escape  from  very  many 
bodies,  and  are  diffused  through  the  air.     These    particles 
excite  the  nerves  of  smell,  which  transmit  the  impressions 
made  on  them  to  the  brain.      To  facilitate  th'e  perception  of 
odors,  the  nostrils  are  placed  in  the  course  of  the  respiratory 
passages,  so  that  all  the  odors  which  are  diffused  in  the  a;r 
inspired,  pass  over  the  pituitary  membrane. 

109.  The  acuteness  of  the  sense  of  smell  depends  on  the 
extent  to  which  the  membrane  is  developed.     Man  is  not  so 
well  endowed  in  this  respect  as  many  animals,  which  have 
the  internal  surface  of  the  nostrils  extremely  complicated,  as 
it  is  especially  among  the  beasts  of  prey. 

110.  The  sense  of  smell  in  Reptiles  is  less  delicate  than 
in  the  mammals  ;  the  pituitary  membrane,  also,  is  less  de- 
veloped.     Fishes   are    probably   still    less   favored    in    this 
respect.     As  they  perceive  odors  through  the  medium  of 
water,    we    should    anticipate    that    the    structure   of   their 
apparatus  would   be  different  from   that  of  animals   which 
breathe  in  the  air.    Their  nostrils  are  mere  superficial  pouch- 
es, lined  with  a  membrane  gathered  into  folds  which  gen- 
erally radiate  from  a  centre,  but  are  sometimes  arranged 
in  parallel  ridges  on  each  side  of  a  central  band.     As   'he 
perfection    of    smell    depends    on    the    amount    of    surface 
exposed,   it   follows    that   those    fishes   which    have    these 
folds  most  multiplied  are  also  those  in  which  fiis  sense  is 
most  acute. 

6 


62  SPECIAL    SENSES. 

111.  No  special  apparatus  for  smell  has  yet  been  found  in 
Invertebrates.     And  yet  there  can  be  no  doubt  that  insects, 
crabs,  and  some  moliusks  perceive  odors,  since   they  are 
attracted  from  a  long  distance  by  the  odor  of  objects.     Some 
of  these  animals  may  be  deceived  by  odors  similar  to  those 
of  their  prey ;  which  clearly  shows  that  they  are  led  to  it  by 
this  sense.     The  carrion  fly  will  deposit  its  eggs  on  plar  ts 
which  have  the  smell  of  tainted  flesh. 

4.     Of  Taste. 

112.  TASTE  is  the  sense  by  which  the  flavor  of  bodies  is 
perceived.     That  the  flavor  of  a  body  may  be  perceived,  it 
must  come  into  immediate  contact  with  the  nerves  of  taste  ; 
these  nerves  are  distributed  at  the  entrance  to  the  digestive 
tube,  on  the  surface  of  the  tongue  and  the  palate.     By  this 
sense,  animals  are  guided  in  the  choice  of  their  food,  and 
warned  to  abstain  from  what  is  noxious.     There  is  an  inti- 
mate connection  between  the  taste  and  the  smell,  so  that 
both  these  senses  are  called  into  requisition  in  the  selection 
of  food. 

113.  The  nerves  of  taste  are  not  so  strictly  special  as 
those  of  sight  and  hearing.     They  do  not  proceed  from  one 
single  trunk,  and,  in  the  embryo,  do  not  correspond  to  an 
isolated  part  of  the  brain.    The  tongue,  in  particular,  receives 
nerves-from  several  trunks;  and  taste  is  perfect  in  proportion 
as  the  nerves  which  go  to  the  tongue  are  more  minutely  dis- 
tributed.    The  extremities  of  the  nerves  generally  terminate 
in  little  asperities  of  the  surface,  called  papilla.     Sometimes 
these  papillae  are  very  harsh,  as  in  the  cat  and  the  ox ;  and 
again  they  are  very  delicate,  as  in  the  human  tongue,  in  that 
of  the  dog,  horse,  &c. 

114.  Birds  have  the  tongue  cartilaginous,  sometimes  be- 
set   with    little   stiff  points;    sometimes   fibrous   or   fringed 
at   the    edges.      In    the   parrots,    it   is    thick   and    fleshy 


OF    TOUCH.  63 

or  it  is  even  barbed  at  its  point,  as  in  the  woodpeckers. 
In  some  reptiles,  the  crocodile  for  example,  the  tongue 
is  adherent ;  in  others,  on  the  contrary,  it  is  capable  of 
extensive  motion,  and  serves  as  an  organ  of  touch,  as  in  the 
serpents,  or  it  may  be  thrust  out  to  a  great  length  to  take 
prey,  like  that  of  the  chameleon,  toad,  and  frog.  In  fishes, 
it  is  usually  cartilaginous,  as  in  birds,  generally  adherent,  and 
its  surface  is  frequently  covered  with  teeth. 

115.  It   is  to  be  presumed,  that  in  animals  which  have  a 
cartilaginous  tongue,  the  taste  must  be  very  obtuse,  especial- 
ly in  those  which,  like   most  fishes,  and  many   granivorous 
birds,  swallow  their   prey  without  mastication.     In  fishes, 
especially,  the  taste  is  very  imperfect,  as  is  proved  by  thcil 
readily  swallowing  artificial  bait.     It  is  probable  that  they 
are    guided    in    the  choice  of   their  prey  by  sight,  rathei 
than  by  taste  or  smell. 

116.  Some  of  the  inferior  animals  select  their  food  with 
no  little   discernment.     Thus,  flies   will  select   the   sugary 
portions  of  bodies.     Some   of   the   mollusks,  as  the   snails 
for  example,  are  particularly  dainty  in  the  choice   of  their 
food.     In  general,  the   taste  is  but  imperfectly  developed, 
except  in  the  mammals,  and    they  are   the   only  animals 
which    enjoy   the    flavor   of  their    food.     With   man,   this 
sense,  like  others,  may  be    greatly  improved  by  exercise  ; 
and  it  is  even  capable  of  being  brought  to  a  high  degree 
of  delicacy. 

* 

5.    Of  Touch. 

117.  The  cense  of  TOUCH  is  merely  a  peculiar  manifesta- 
tion  of  the   general    sensibility,  seated   in    the    skin,   and 
dependent  upon  the  nerves  of  sensation,  which  expand  over 
the  surface  of  the  body.     By  the  aid  of  this  general  sensi- 
bility, we  leavn  whether  a  body  is  hot  or  cold,  wet  or  dry. 
We  may  also,  by  simple  contact,  gain  an  idea,  to  a  certain 


64  SPECIAL    SENSES. 

extent,  of  the  form  and  consistence  of  a  body,  as,  for  exam* 
pie,  whether  it  be  sharp  or  blunt,  soft  or  hard. 

118.  This  faculty  resides  more  especially  in  the   hand, 
which  is  not  only  endowed  with  a  more  delicate  tact,  but, 
owing  to  the  disposition  of  the  fingers,  and  the  opposition  of 
the  thumb  to  the  other  fingers,  is  capable  of  so  moulding 
itself  around  objects,  as  to  multiply  the  points  of  contact. 
Hence,  touch  is  an  attribute  of  man,  rather  than  of  other 
animals ;   for  among  these  latter,  scarcely  any,  except  the 
monkeys,  have  the  faculty  of  touch  in  their  hands,  or,  as  it 
is  technically  termed,  of  palpation. 

119.  In  some  animals,  this  faculty  is  exercised  by  other 
organs.     Thus  the  trunk  of  the  elephant  is  a  most  perfect 
organ  of  touch  ;  and  probably  the  mastodon,  whose  numer- 
ous relics  are  found  scattered  in  the  superficial  layers  of 
the    earth's    crust,    was    furnished  .  with    a   similar    organ. 
Serpents    make    use    of    their   tongue    for   touch ;    insects 
employ  their  palpi,  and  snails  their  tentacles,  for  the  same 
purpose. 

6.    The   Voice. 

120.  Animals  have    not  only  the   power  of  perceiving, 
but    many   of  them   have    also   the   faculty   of  producing 
sounds  of  every  variety,  from  the  roaring  of  the  lion  to  the 
song  of  the  bird  as  it  salutes  the  rising  sun.     It  is  moreover 
to  be  remarked  that  those  which  are  endowed  with  a  voice, 
likewise  have  the  organ  of  hearing  well  developed. 

121.  Animals  employ  their  voice  either  for  communica- 
tion with  each  other,  or  to  express  their  sensations,  their  en- 
joyments, their  sufferings.     Nevertheless,  this  faculty  «  en 
joyed  Bby  but  a  small  minority  of  animals ;  with  but  very 
few  exceptions,  only  the  mammals,   the  birds,  and  a  few 
reptiles    are    endowed   with    it.      All    others    are    dumb. 
Worms  ard  insects  have  no  true  voice ;  for  we   must  not 


OF    THE    VOICE,  65 

mistake  for  it  the  buzzing  of  the  bee,  which  is  merely  a 
noise  created  by  the  vibration  of  the  wings  ;  nor  the  grating 
shriek  of  the  Locust,  (grasshopper,)  caused  by  the  friction  of 
his  legs  against  his  wings  ;  nor  the  shrill  noises  of  the  cricket, 
or  the  tell-tale  call  of  the  katydid,  produced  by  the  friction 
of  the  wing  covers  upon  each 'other,  and  in  numerous  similai 
cases  which  might  be  cited. 

122.  Consequently,  were  the  mammals,  the  birds,  and  the 
frogs  to  be  struck  out  of  existence,  the  whole  Animal  King- 
dom would  be  dumb.     It  is  difficult  for  us,  living  in  the  midst 
of  the  thousand  various  sounds  which  strike  our  ear  from  all 
sides,  to  conceive   of  such  a  state.     Yet  such  a  state  did 
doubtless  prevail  for  thousands  of  ages,  on  the  surface  of  our 
globe,  when   the  watery  world  alone  was  inhabited,  and  be- 
fore man,  the  birds,  and  the  mammals  were  called  into  being. 

123.  In  man  and  the  mammals,  the  voice  is  formed  in  an 
organ  called  the  larynx,  situated  at  the  upper  part  of  the 
windpipe,  below  the  bone  of  the  tongue,  (a.)     \ 

The   human   larynx,  the  part  called  Adam's 

apple,    is   composed   of  several   cartilaginous 

pieces,  called  the  thyroid  cartilage,    (&,)  the        ^^_?:^. 

cricoid  cartilage,  (c,)  and  the  small  arytenoid 

cartilages.     Within  these  are  found  two  large 

folds  of  elastic  substance,  known  by  the  name        Fig.  22. 

of  the  vocal  cords,  (m.)     Two  other   analogous  folds,  the 

superior  ligaments  of  the  glottis,   (n,)  are  situated   a   little 

above  the  preceding.     The  glottis  (o)  is  the  space  between 

these  four  folds.     The  arrangement  of  the  vocal  cords,  ana 

of  the  interior  of  the  glottis  in   man,  is  indicated  by  dotted 

lines,  in  Fig.  22. 

124.  The  mechanism  of  the  voice  is  as  follows :  the  air, 
o-  its  way  to  the  lungs,  passes  the  vocal  cords.     So  long  as 
these  are  in  repose,  no  sound  is  produced ;  but  the  mome  it 
they  are  made  tense  they  narrow  the  aperture,  and  oppose 

6* 


66 


OF    THE    VOICE. 


an  obstacle  to  the  current  of  air,  and  it  cannot  pass  without 
causing  them  to  vibrate.  These  vibrations  produce  the 
voice ;  and  as  the  vocal  cords  are  susceptible  of  different 
degrees  of  tension,  these  tensions  determine  different  sounds  ; 
giving  an  acute  tone  when  the  tension  is  great,  but  a  grave 
and  dull  one  when  the  tension  is  feeble. 

125.  Some    mammals    have,    in    addition,   large   cavities 
which  communicate  with  the  glottis,  and  into  which  the  air 
reverberates,  as  it  passes  the   larynx.     This  arrangement  is 
especially  remarkable  in  the  howling  monkeys,  which  are  dis- 
tinguished above  all  other  animals  for  their  deafening  howls. 

126.  In  birds,  the  proper  larynx  is  very  simple,  destitute 
of  vocal  cords,  and  incapable  of  producing  sounds  ;  but  at 
the  lower  end  of  the  windpipe  there  is  a  second  or  inferior 
larynx,  which  is  very  complicated  in  structure.     It  is  a  kind 

of  bony  drum,  (a,)  having  with- 
in it  two  glottides,  formed  at  the 
top  of  the  two  branches  (bb)  of 
the  windpipe,  (c,)  each  provided 
with  two  vocal  cords.  The  dif- 
ferent pieces  of  this  apparatus 
are  moved  by  peculiar  muscles, 
the  number  of  which  varies  in 
different  families.  In  birds  which 
have  a  very  monotonous  cry, 
such  as  the  gulls,  the  herons, 
the  cuckoos,  and  the  mergansers 

(Fig.  23,)  there  is  but  one  or  two  pairs  ;  parrots  have  three 

and  the  birds  of  song  have  five. 

127.  Man  alone,  of  all  the  animal  creation,  has  the  power 
of  giving  to  the  tones  he  utters  a  variety  of  definite  or  ar- 
ticulate sounds ;  in  other  words,  he  alone  has  the  gift  of 
speech. 


Fig.  23. 


V 


CHAPTER    FOURTH. 

OF    INTELLIGENCE    AND    INSTINCT. 

128.  BESIDES  the  material  substance  of  which  the  body  is 
constructed,  there  is  also  an  immaterial  principle,  which, 
though  it  eludes   detection,    is  none   the  less  real,  and  to 
which  we  are  constantly  obliged  to  recur  in  considering  the 
phenomena  of  life.     It  originates  with  the  body,  and  is  de- 
veloped with  it,  while  yet  it  is  totally  apart  from  it.     The 
study  of  this  inscrutable   principle    belongs  to  one  of   the 
highest  branches  of  Philosophy  ;  and  we  shall  here  merely 
allude  to  some  of  its  phenomena  which  elucidate  the  devel- 
opment and  rank  of  animals. 

129.  The  constancy  of  species  is  a  phenomenon  depend- 
ing on   the  immaterial    nature.     Animals,  and  plants  also, 
produce  their  kind,  generation  after  generation.     We  shall 
hereafter  show  that  all  animals  may  be  traced  back,  in  the 
embryo,  to  a  mere  point  in  the  yolk  of  the  egg,  bearing 
no  resemblance  whatever  to  the  future  animal  ;  anJ  no  in- 
spection would  enable  us  to  declare  with  certainty  what  that 
animal   is  to  be.     But   even    here  an  immaterial  principle 
is  present,  which  no  external  influence  can  essentially  modify, 
and  determines  the  growth  of  the  future  being.    The  egg  of 
the  hen,  for  instance,  cannot  be  made  to  produce  any  other 
animal  than  a  chicken,  and  the  egg  of  the  codfish  produces 
only  the  cod.  .  It  may  therefore  be  said  with  truth,  that  the 
chicken  and  the  cod  existed  in  the  egg  before  their  formation 
as  such. 

130.  PERCEPTION  is  a  faculty  springing  from  this  princi- 
ple,   The  organs  of  sense  are  the  instruments  for  receiving 


68  INTELLIGENCE    AND    INSTINCT. 

sensations,  but  they  are  not  the  faculty  itself,  without, 
which  they  would  be  useless.  We  all  know  that  the 
eye  and  ear  may  be  open  to  the  sights  and  sounds  about 
us;  but  if  the  mind  happens  to  be  preoccupied,  we  perrei»e 
them  not.  We  may  even  be  searching  for  something  which 
actually  lies  within  the  compass  of  our  vision;  the  light 
enters  the  eye  as  usual,  and  the  image  is  formed  on  the 
retina  ;  but,  to  use  a  common  expression,  we  look  without 
seeing,  unless  the  mind  that  perceives  is  directed  to  the  object. 

131.  In  addition  to  the  faculty  of  perceiving  sensations, 
the  higher  animals  have   also  the   faculty  of  recalling  past 
impressions,  or  the  power  of  memory.     Many  animals  retain 
a  recollection   of   the    pleasure  or   pain  they   have   experi- 
enced, and  seek  or  avoid  the  objects  which  may  have   pro- 
duced these  sensations  ;  and,  in  doing  so,  they  give  proof 
of  judgment. 

132.  This  fact  proves  that  animals  have  the  faculty  of 
comparing  their  sensations  and  of  deriving  conclusions  from 
them  ;  in    other  words,  that  they   carry   on  a   process   of 
reasoning. 

133.  -These  different  faculties,  taken  together,  constitute 
intelligence.     In  man,  this   superior  principle,  which  is  an 
emanation  of  the  divine  nature,   manifests    itself  in    all  its 
splendor.     God  u  breathed  into  him  the  breath  of  life,  and 
man  became  a  living  soul."    It  is  man's  prerogative,  and  his 
alone,  to  regulate  his  conduct  by  the  deductions  of  reason, 
he  has    the    faculty  of  exercising  his  judgment   not   only 
upon  the  objects  which  surround  him,  and  of  apprehending 
the  many  relations  which  exist  between  himself  and  the  ex- 
ternal  world;  he  may  also  apply  his  reason. to  immaterial 
things,   observe   the  operations  of  his  own  intellect,  and,  by 
the  'analysis  of  his  faculties,  may  arrive  at  the  conscious- 
ness  of  his  own  nature,  and  even  conceive  of  that  Infinite 
Spirit,  "  whom  none  by  searching  can  find  out." 


INTELLIGENCE  AND  INSTINCT  69 

134.  Other  animals  cannot  aspire  to  conceptions  of  this 
kind  ,  they  perceive  only  such  objects  as  immediately  strike 
their  senses,  and  are  incapable  of  continuous  efforts  of  the 
reasoning  faculty  in  regard  to  them.     But  thei    conduct  is 
frequently  regulated   by  another  principle  of  inferior  order 
still  derived  from  the  immaterial  principle,  called  INSTINCT. 

135.  Under  the  guidance  of  Instinct,  animals  are  enabled 
to  perform    certain  operations,  without  instruction,  in    one 
undeviating  manner.     When  man  chooses  wood  and  stone, 
as  the  materials  for  his  dwelling,  in  preference  to  straw  and 
leaves,  it  is  because  he  has  learned  by  experience,  or  be- 
cause his  associates  have  informed  him,  that  these  materials 
are  more  suitable  for  the  purpose.     But  the  bee  requires  no 
instructions  in  building  her  comb.     She  selects  at  once  the 
fittest  materials,  and  employs  them  with  the  greatest  econo- 
my ;  and  the  young  bee  exhibits,  in  this  respect,  as  much 
discernment  as  those   who  have   had    the    benefit   of  long 
experience.     She  performs  her  task  without  previous  study, 
and,  to  all  appearances,  without   the   consciousness  of  its 
utility,  being  in  some  sense  impelled  to  it  by  a  blind  impulse. 

136.  If,  however,  we  judge  of  the   instinctive  acts  of  ani- 
mals when  compared  with  acts  of  .intelligence,  by  the  relative 
perfection  of  their  products,  we  may  be  led  into  gross  errors, 
as  a  single  example  will  show.     No  one  will  deny  that  the 
honey-comb  is  constructed  with  more  art  and  care  than  the 
huts  of  many  tribes  of  men.     And  yet,  who  would  presume 
to  conclude  from   this  that  the  bee  is  superior  in  intelligence 
to  the  inhabitant  of  the  desert  or  of  the  primitive  forest  ? 
It  is  evident,  on  the  contrary,  that  in  this  particular  case  we 
are  not  to  judge  of  the  artisan  by  his  work.     As  a  work  of 
man,  a  structure  as  perfect  in  all  respects  as  the  honey-comb 
would    indicate   very   complicated    mental    operations,   and 
probably  would  require  numerous  preliminary  experiments. 

137.  The  instinctive  actions  of  animals  relate  either  to 


70  INTELLIGENCE    A!  ID    INSTINCT. 

the  procuring  of  food,  or  to  the  rearing  of  their  young ;  m 
other  words,  they  have  for  their  end  the  preservation  of  .the 
individual  and  of  the  species.  It  is  by  instinct  that  the 
leopard  conceals  himself  and  awaits  the  approach  of  his 
prey.  It  is  equally  by  instinct  that  the  spider  spreads  his 
web  to  entangle  the  flies  which  approach  it. 

138.  Some  animals  go   beyond  these  immediate  precau- 
tions ;  their  instinct  leads  them  to  make  provision  for  the 
future.     Thus   the  squirrel   lays    in  his  store  of  nuts   and 
acorns   during   autumn,  and  deposits   them    in  cavities  of 
trees,  which  he  readily  finds  again  in  winter.     The  hamster 
digs,  by  the  side  of  his  burrow,  compartments  for  magazines, 
which  he  arranges  with  much  art.     Finally,  the  bee,  more 
than  any  other  animal,  labors  in  view  of  the  future ;  and 
she  has  become  the  emblem  of  order  and  domestic  economy. 

139.  Instinct  exhibits  itself,  in  a  no  less  striking  manner, 
in  the  anxiety  which  animals   manifest  for  the  welfare  of 
their   anticipated    progeny.     All   birds  build   nests  for   the 
shelter  and  nurture  of  their  young,  and  in  some  cases  these 
nests  are  made  exceedingly  comfortable.     Others  show  very 
great  ingenuity  in  concealing  their  nests  from  the  eyes  of 
their   enemies,   or   in   placing    them    beyond    their   reach 
There  is  a  small   bird  in  the   East  Indies,  the  tailor  bird 
(Sylvia  sutoria,)  which  works  wool  or  cotton  into  threads 
with  its  feet  and  beak,  and  uses  it  to  sew  together  the  leaves 
of  trees  for  its  nest. 

140.  The  nest  of  the  fiery  hang-bird,  (Icterus  Baltimore,) 
dangling  from  the  extremity  of  some  slender,  inaccessible 
twig,  is  familiar  to  all.     The  beautiful  nest  of  the  humming- 
bird, seated  on  a  mossy  bough,  and  itself  coated  with  lichen 
and  lined  with  the  softest  down  from  the  cotton-grass  or  tho 
mullein  leaf,  is  calculated   equally  for  comfort  and  for  es- 
caping observation.     An  East  Indian  bird,  (Ploceus  Philippi- 
uus,)  mt  only  exhibits  wonderful  devices  in  the  construction, 


INTELLIGENCE    AND    INSTINCT.  71 

security,  and  comfort  of  its  nest,  but  displays  a  still  furthel 
advance  towards  intelligence.  The  nest  is  built  at  the  tips 
of  long  pendulous  twigs,  usually  hanging  over  the  water.  It 
is  composed  of  grass,  in  such  a  manner  as  to  form  a  com- 
plete thatch.  The  entrance 
is  through  a  long  tube,  run- 
ning downwards  from  the 
edge  of  the  nest ;  and  its 
lower  end  is  so  loosely  woven, 
that  any  serpent  or  squirrel, 
attempting  to  enter  the  aper- 
ture, would  detach  the  fibres, 
and  fall  to  the  ground.  The 
mule,  however,  who  has  no 
occasion  for  such  protection, 
builds  his  thatched  dome,  sim- 
ilar to  that  of  the  female,  and  FiS-  24- 
by  its  side ;  but  makes  simply  a  perch  across  the  base  of 
the  dome,  without  the  nest-pouch  or  tube. 

141.  But  it  is  among  insects  that  this  instinctive   solici- 
tude for  the  welfare  of  the  progeny  is  every  where  exhibited 
in    the  most   striking   manner.     Bees   and  wasps   not   only 
prepare  cells  for  each  of  their  eggs,  but  take  care,  before 
closing  the  cells,  to  deposit  in  each  of  them  something  ap- 
propriate for  the  nourishment  of  the  future  young. 

142.  It  is  by  the  dictate  of  instinct,  also,  that  vast  numbers 
of  animals  of  the  same  species  associate,  at  certain  periods 
of  the  year,  for  migration  from  one  region  to  another ;  as 
the  swallows  and  passenger  pigeons,  which  are  sometimes 
met  with  in  countless  flocks. 

143.  Other  animals  live  naturally  in  large  societies,  and 
labor  in  common.     This  is  the  case  with  the  ants  and  bees. 
Among  tin  latter,  even  the  kind  of  labor  for  each  member 
of  the    community    is    determined    beforehand,   by  instinct. 


72  INTELLIGENCE    AND    INSTItfflfN 

Some  of  them  collect  only  honey  and  wax ;  while  others 
are  charged  with  the  care  and  education  of  the  young ;  and 
still  others  are  the  natural  chiefs  of  the  colony. 

144.  Finally,  there  are  certain  animals  so  guided  by  their 
instinct   as    to   live    like    pirates,  on   the   avails  of  others* 
labor.     The   Lestris  or  Jager  will    not   take   the  trouble  to 
catch  fish  for  itself,  but  pursues  the  gulls,  until,  worn  out 
by  tKe  pursuit,  they  eject  their  prey  from  their  crop.     Some 
ants  make  war  upon  others  less  powerful,  take  their  young 
away  to  their  nests,  and  oblige  them  to  labor  in  slavery. 

145.  There  is  a  striking  relation  between  the  volume  of' 
ihe  brain  compared  with  the  body,  and  the  degree  of  intelli- 
gence which  an  animal  may   attain.     The  brain  of  man  is 
the  most  voluminous  of  all,  and  among  other  animals  there  is 
every  gradation  in.  this  respect.     In  general,  an  animal  is  the 
more  intelligent,  in  proportion  as  ;ts  brain  bears  a  greater 
resemblance  to  that  of  man. 

146.  The    relation    between    instinct    and    the    nervous 
system  does   not  present  so  intimate   a  correspondence   as 
exists  between  the  intellect  and  the  brain.   .  Animals  which 
have  a  most  striking  development  of  instinct,  as  the  ants  and 
bees,  belong  to  a  division  of  the  Animal  Kingdom  where  the 
nervous  system  is  much  less  developed  than  that  of  the  ver- 
tebrates, since  they  have  only  ganglions,  without  a  proper 
brain.     There  is  even  a  certain  antagonism  between  instinct 
and  intelligence,  so  that  instinct  loses  its  force  and   peculiar 
character,  whenever  intelligence  becomes  developed. 

147.  Instinct  plays  but  a  secondary  part  in  man.     He  is 
not,  however,  entirely  devoid  of  it.     Some  of  his  actions  are 
entirely  prompted  by  instinct,  as,  for  instance,  the  attempts  of 
the  infant  to  nurse.     The  fact,  again,  that  these  instinctive 
actions  mostly  belong  to  infancy,  when   intelligence   is  but 
slightly  developed,  goes  to  confirm  the  two  last  propositions, 

* 


CHAPTER    FIFTH 

OF  MOTION. 
SECTION    I. 

APPARATUS    OF    MOTION. 

148.  THE  power  of  voluntary  motion  is  the  second  grand 
characteristic  of  animals,  (57.)     Though  they  may  not  all 
have  the  means  of  transporting  themselves  from   place  to 
place,  there-is  no  one  which  has  not  the  power  of  executing 
some  motions.     The  oyster,  although  fixed  to  the  ground, 
opens  and  closes  its  shell  at  pleasure  ;  and  the  little  coral 
animal  protrudes  itself  from   its  cell,  and   retires  again  at 
its  will. 

149.  The  movements  of  animals  are  effected  by  means  of 
muscles,  which  are  organs  designed   expressly  for  this  pur- 
pose, and  which  make  up  that  portion  of  the  body  which 
is  commonly  called  flesh.     They  are  composed  of  threads, 
which   are    readily  seen   in   boiled   meat.      These  threads 
are  again  composed  of  still  more  delicate  fibres,  called  mus- 
cular fibres,  (45,)    which   have  the  property  of  elongating 
and  contracting. 

150.  The  motions  of  animals  and  plants  depend,  therefore, 
upon  causes  essentially  different.     The  expansion  and  closing 
of  the  leaves  and  blossoms  of  plants,  which  are  their  most 

7 


74  APPARATUS)    OF    MOTION. 

obvious  motions,  are    due   to  the  influence   ,  f  ligl.  ,   heal 
moisture,  cold,  and  similar  external  agents  ;  but  all  the  mo 
tions  peculiar  to  animals  are  produced   by  a  cause  residing 
within   themselves,    namely,  the    contractility    of  muscular 
fibres. 

151.  The  cause  which  excites  contractility  resides  in  the 
nerves,    although    its    nature   is    not   precisely    understood. 

We  only  know  that  each 
muscular  bundle  receives 
one  or  more  nerves,  whose 
filaments  pass  at  intervals 
across  the  muscular  fibres, 
as  seen  in  Fig.  25.  It  has 
also  been  shown,  by  experi- 
ment, that  when  a  nerve 
Fig.  25. 

entering  a  muscle  is  sev- 
ered, the  muscle  instantly  loses  its  power  of  contracting 
under  the  stimulus  of  the  will,  or,  in  other  words,  is  par- 
alyzed. 

152.  The  muscles  may  be  classified,  according  as  they 
are  more  or  less  under  the  control   of  the  will.     The  con- 
tractions of  some  of  them  are  entirely  dependent  on  the  will, 
as  in  the  muscles  of  the  limbs  used  for  locomotior .    Others 
are  quite  independent  of  it,  like  the  contractions  of  the  heart 
and  stomach.    The  muscles  of  respiration  ordinarily  act  inde- 
pendently  of  the  will,  but  are  partially  subject  to  t :   thus, 
when  we  attempt  to  hold   the  breath,  we  arrest,  for  the  mo- 
ment, the  action  of  the  diaphragm. 

153.  In  the  great   majority  of  animals,  motion  is  greatiy 
aided  by   the  presence  of  solid  parts,   of  a  bony  or  horny 
structure,    which  either   serve  as  firm   attachments  to    the 
muscles,  or,   being   arranged  so  as  to  act  as  levers,  to  in- 
crease the  precision  and  sometimes  the  force  of  movements. 
The  solid  parts  are  usually  so  arranged  as  to  form  a  sub- 


APPARATUS    OF    MOTION.  75 

stuntial  framework  for  the  body,  which  has  heen  varioi  sly 
designated  in  the  several  classes  of  animals,  as  the  test,  shell 
carapace,  skeleton,  fyc.  The  study  of  these  parts  is  one  of  the 
most  important  branches  of  comparative  anatomy.  Their 
characters  are  the  most  constant  and  enduring  of  all  others. 
Indeed,  these  solid  parts  are  nearly  all  that  remains  of 
tue  numerous  extinct  races  of  animals  of  past  geological 
eras  ;  and  from  these  alone  are  we  to  determine  the  struc- 
ture and  character  of  the  ancient  fauna. 

154.  Most  of  the  Radiata  have  a  calcareous  test  or  crust) 
shell.     In  the  Polypi,  this  structure,  when  it  exists,  is  usually 
very  solid,  sometimes  assuming  the  form  of  a  simple  inter- 
nal   skeleton,   or  forming   extensively   branched   stems,   as 
in  the   sea-fans ;  or  giving  rise  to  solid    masses,   furnished 
with  numerous  cavities  opening  at  the  surface,  from  which 
the  movable  parts  of  the  animals  are  protruded,  with  the 
power,  however,  of  retracting  themselves  at  pleasure,  as  in 
the  corals.     In  the  Echinoderms,  the  test  is  intimately  con- 
nected with  the  structure  of  the  soft 

parts.  It  is  composed  of  numer- 
ous little  plates,  sometimes  con- 
solidated and  immovable,  as  in 
the  sea-urchins,  (Fig.  26,)  and 
sometimes  so  combined,  as  to 
allcw  of  various  motions,  as  in 
the  star-fishes,  (Fig.  17,)  which  use  their  projecting  rays, 
both  for  crawling  and  swimming. 

155.  In  the  Mollusks,  the  solid   parts  are  secreted  by  the 
skin,  most  frequently  in  the  form  of  a  calcareous  shell  of 
one,  two,  or  many  pieces,  serving  for  the  protection  of  the 
soft  parts  which  they  cover.     These  shells  are  geneially  so 
constructed  as  to  afford   complete   protection  to  the  animal 
within  their  cavities.     In  a  few,  the  shell  is  too  small  for  this 
purpose  ;  and  in  some  it  exists  only  at  a  very  early  period. 


76  APPARATUS    OF    MOTION. 

and  is  lost  as  the  animal  is  developed,  so  that  at  last  nere  is 
no  other  covering  than  a  slimy  skin.  In  others,  the  skin 
becomes  so  thv^k  and  firm  as  to  have  the  consistence  of 
elastic  leather  ;  or  it  is  gelatinous  or  transparent,  and,  what  is 
very  curious,  these  tissues  may  be  the  same  as  those  of  woody 
fibre,  as,  for  example,  in  the  Ascidia.  As  a  general  thing, 
the  solid  parts  do  not  aid  in  locomotion,  so  that  the  mol- 
lusks  are  mostly  sluggish  animals.  It  is  only  in  a  few  rare 
cases  that  the  shell  becomes  a  true  lever,  as  in  the  Scollops, 
(Pecten,)  which  use  their  shells  to  propel  themselves  in 
swimming. 

156.  The  muscles  of  mollusks  either  form  a  flat  disk  un- 
der the  body,  or  large   bundles  across  its  mass,  or  are  dis- 
tributed in  the  skin  so  as  to   dilate  and  contract  it,  or  are 
arranged  about  the  mouth    and  tentacles,  which   they  put 
in  motion.     However  varied  the  disposition  may  be,  they 
always  form  very  considerable  masses,  in  proportion  to  the 
size  of  the  body,   and  have  a  soft  and  mucous  appearance, 
such  as  is  not  seen  in  the  contractile  fibres  of  other  animals. 
This  peculiar  aspect   no    doubt   arises   from  the  numerous 
small  cavities  extending  between  the  muscles,  and  the  secre- 
tion of  mucus  which  takes  place  in  them. 

157.  In  the  Articulated  animals,  the  solid  parts  are  ex- 
ternal, in  the  form  of  rings,  generally  of  a  horny  structure, 
but  sometimes  calcareous,  and  successively  fitting  into  each 
other  at  their  edges.     The  tail  of  a  lobster  gives  a   good 
idea    of  this   structure.      The    rings  differ  in  the    severa 
classes  of  this  department,  merely  as  to  volume,  form,  solid- 
ity, number  of  pieces,  and  the  degree  of  motion  which  one 
has  upon  another.     In  some  groups  they  are  consolidated,  so 
as  to  form    a  shield  or  carapace,  such  as  we  see  in  the 
crabs.      In  others,  they  are  membranous,  and  the  body  is 
capable  of  assuming  various  forms,   as  in   the  leeches   and 
worms  generally 


APPARATUS    OF    MOTION. 


77 


158.  A   variety  of   appendages   are    attached    to    these 
rings,  such  as  jointed  legs,  or  in  place  of  them  stiff  bristles 
oars  fringed  with  silken  threads,  wings  either  firm  or  mem 
branous,  antennae,  movable  pieces  which  perform  the  office 
of  jaws,  &c.     But  however  diversified    this  solid  apparatus 
may  be,  it  is  universally  the  case  that  the  rings,  to  which 
every  segment  of  the  body  may  be  referred  as  to  a  type,  com-, 
bine  to  form  but  a  single  internal  cavity,  in  which  all  the  or- 
gans are  enclosed,  the  nervous  system,  as  well  as  the  organs 
of  vegetative  life,  (63.) 

159.  The  muscles  which  move 
all  these  parts  have  this  peculiar- 
ity, that  they  are  all  enclosed  with- 
in the  more  solid  framework,  and 
not  external  to  it,  as  in  the  verte- 
brates ;  and  also  that  the  muscular 
bundles,  which  are  very  consider- 
able in  number,  have  the  form  of 
ribbons,  or  fleshy  strips,  with  par- 
allel fibres  of   remarkable  white- 
ness.    Figure   27    represents  the 


Fig.  27. 


disposition  of  the  muscles  of  the  caterpillar  which  destroys 
the  willow,  (Cossus  ligniperda.)  The  right  side  represents 
the  superficial  layer  of  muscles,  and  the  left  side  the  deep- 
seated  layer. 

160.  The  Vertebrata,  like  the  articulated  animals,  have 
solid  parts  at  the  surface,  as  the  hairs  and  horns  of  mam- 
mais,  the  coat  of  mail  of  the  armadillo,  the  feathers  and  claws 
of  birds,  the  bucklers  and  scales  of  reptiles  and  fishes,  &c. 
Hut  they  have  besides  this,  along  the  interior  of  the  whole 
body,  a  solid  framework  not  found  in  the  invertebrates,  well 
known  as  the  SKELETON. 

161.  T.he  skeleton  is  composed  of  a  series  of  separate 
bpnes    called  vertebras,  united  to  each  other  by  ligaments. 

7* 


78 


APPARATUS    OF    MOTION. 


Each  vertebra  has  a  solid  centre  with  four  branches,  two  of 
which  ascend  and  form  an  arch  above, 
and  two  descend,  forming  an  arch  below 
the  body  of  the  vertebra.  The  upper 
arches  form  a  continuous  cavity  (a)  along 
the  region  of  the  trunk,  which  encloses 
the  spinal  marrow,  and  in  the  head  re- 
ceives the  brain,  (frh)  The  lower  arches 
(b)  form  another  >cavity,  similar  to  the 
superior  one,  which  contains  the  organs  of 
nutrition  and  reproduction  ;  their  branch- 
es generally  meet  below,  and  when  dis- 
joined, the  deficiency  is  supplied  by 
fleshy  walls.  Every  part  of  the  skeleton 
may  be  reduced  to  this  fundamental  typt 
the  vertebra,  as  will  be  shown,  when  treating  specially  of  the 
vertebrate  animals ;  'so  that  between  the  pieces  composing 
the  head,  the  trunk,  or  the  tail,  we  have  only  differences 
in  the  degree  of  development  of  the  body  of  the  ver- 
tebra, or  of  its  branches,  and  not  in  reality  different  plans 
of  organization. 

162.    The  muscles  which  move  this  solid  framework  of 
the   vertebrata    are    disposed    around    the   vertebra?,   as    is 


Fig.  28. 


Fig.  29. 

woll  exemplified  among  the  fishes,  where  there  is  a   band 
of   muscles    for   each   vertebra.      In    proportion    as    limbs 


LOCOMOTION. 


79 


are  developed,  this  intimate  relation  between  the  muscles 
and  the  vertebrae  diminish- 
es. The  muscles  are  un- 
equally distributed  and  are 
concentrated  about  the 
limbs,  where  the  greatest 
amount  of  muscular  force 
is  retired.  For  this  rea- 
son, the  largest  masses  of 
flesh  in  the  higher  verte- 
brates are  found  about  the 
shoulders  and  hips ;  while 
in  fishes  they  are  concen- 
trated about  the  base  of  the  Fig.  30. 
tail,  which  is  the  part  principally  employed  in  locomotion. 


SECTION  II. 


OF    LOCOMOTION. 

163.  One  of  the  most  curious  and  important  applic  it  ions 
of  this   apparatus  of  bones   and    muscles   is  for   LOCOMO- 
TION.    By  this  is  understood  the  movement  which  an  animal 
makes  in  passing  from  place  to  place,  in  the  pursuit  of  pleas- 
ure, sustenance,  or  safety,  m  distinction  from  those  motions 
which  are  performed  equally  well  while  stationary,  such  as 
the  acts  of  respiration,  mastication,  &c. 

164.  The  means  which  nature  has  brought  into  action  to 
effect   locomotion   under  all    the  various   circumstances   in 
which    animals   are    placed,  are  very  diversified ;    and    the 
study  of  their  adaptation  to  the  necessities  of  animals  is  highly 
interesting  in  a  mechanical,  as  well  as  in  a  zoological  point 
of  view.     Two  general  plans  may  be  noticed,  under  which 
these  varieties  may  be  arranged.     Either  the  whole  body  is 


80  LOCOMOTION. 

equally  concerned  in  effecting  locomotion,  or  only  some  of 

its  parts  are  employed  for  the  purpose. 

165.  The  jelly-fishes  (Medusae)  swim 
by  contracting  their  umbrella-shaped 
bodies  upon  the  water  below,  and  its 
resistance  urges  them  forwards.  Other 
animals  are  provided  with  a  sac  or 
siphon,  which  they  may  fill  with  water 
and  suddenly  force  out,  producing  a  jet, 
which  is  resisted  by  the  surrounding 
water,  and  the  animal  is  thus  propelled. 

The  Biche-le-mar,  (Holothuria,)  the  cuttle-fishes,  the  Salpae, 

&c.,  move  in  this  way. 

166.  Others  contract  small  portions  of  the  body  in  suc- 
cession,   which    being    thereby    rendered    firmer,    serve    as 
points  of  resistance,  against  which  the  animal  may  strive, 
in  urging  the  body  onwards.     The  earth-worm,  whose  boJy 
is  composed  of  a  series  of  rings   united   by  muscles,  and 
shutting  more  or  less  into  each  other,  has  only  to  close  up 
the  rings  at  one  or  more  points,  to  form  a  sort  of  fulcrum, 
against  which  the  rest  of  the  body  exerts  itself  in  extending 
forwards. 

167.  Some  have,  at  the  extremities  of  the  body,  a  cup  or 
some  other  organ  for  maintaining  a  firm  hold,  each  extremity 
acting  in  turn  as  a  fixed  point.     Thus  the  Leech  has  a  cup 
or  sucker  at  its  tail,  by  which  it  fixes  itself;  the  body  is  then 

elongated    by  the    contraction 
of  the   muscular  fibres  which 
encircle  the  animal ;  the  mouth 
is  next  fixed  by  a  similar  suck- 
Fig.  32.  er  and  by  the   contraction  of 
muscles  running  lengthwise  the  body  is  shortened,  and  the 
tail,  losing  its  hold,  is  brought  forwards  to  repeat  the  same 
nrocess.     Most  of  the  bivalve  mollusks,  such  as  the  clams. 


LOCOMOTION.  81 

move  from  place  to  place,  in  a  similar  way.  A  fleshy  organ, 
called  the  foot,  is  thrust  forward,  and  its  extremity  fixed 
in  tha  mud,  or  to  some  firm  object,  when  it  contracts, 
and  thus  draws  along  the  body  and  the  shell  enclosing 
it.  Snails,  and  many  similar  animals,  have  the  fleshy  under 
surface  of  their  body  composed  of  an  infinitude  of  very  short 
muscles,  which,  by  successive  contractions,  so  minute,  indeed, 
as  scarcely  to  be  detected,  enable  them  to  glide  along 
smoothly  and  silently,  without  any  apparent  muscular  effort. 

168.  In  the  majority  of  animals,  however,  locomotion  is 
effected  by  means  of  organs  specially  designed  for  the  pur- 
pose.     The   most   simple   are    the    minute,  hair-like    cilia, 
which  fringe   the  body  of   most  of  the    microscopic   infu- 
sory  animalcules,  and  which,  by  their  incessant  vibrations, 
cause    rapid    movements.     The   sea-urchins   and  star-fishes 
have  little  thread-like  tubes  issuing  from  every  side  of  the 
body,  furnished  with    a    sucker  at  the   end.     By  attaching 
these  to  some  fixed  object,  they  are  enabled  to  draw  or  roll 
themselves  along  ;  but  their  progress  is  always  slow.    Insects 
are  distinguished  for  the  number  and  great  perfection  of  their 
organs  of  motion.     They  have  at  least  three  pairs  of  legs, 
and    usually  wings    also.     But    those    that   have   numerous 
feet,  like  the  centipedes,  are   not   distinguished   for  agility. 
The  Crustacea  generally  have    at  least  five  pairs  of   legs, 
which    are    used    for   both 

swimming  and  crawling. 
The  Worms  are  much  less 
active;  some  of  them  have 
only  short  bristles  at  their 
sides.  Some  of  the  marine 
species  use  their  fringe-like  gills  for  paddles.  (Fig.  33.) 

169.  Among  the  Vertebrata,  we  find  the  greatest  diversity 
in  the  organs  of  locomotion  and  the  modes  of  their  applica- 
tion, as  well  as  the  greatest  perfection,  in  whatever  element 


82  ORGANS    OF    LOCOMOTION. 

they  may  be  employed.  The  sailing  of  the  eagle,  the  hound- 
ing of  the  antelope,  the  swimming  of  the  shark,  are  riot 
equalled  by  any  movements  of  insects,  This  superiority  is 
due  to  the  internal  skeleton,  which,  while  it  admits  a  great 
display  of  force,  gives  to  the  motions,  at  the  same  time,  a 
great  degree  of  precision. 

1.     Plan  of  the   Organs  of  Locomotion. 

170.  The  organs  of  progression  in  vertebrated    animals 
nt'ver  exceed  four  in  number,  and  to  them  the  term  limbs  is 
more  particularly  applied.     The  study  of  these  organs,  a3 
characteristic  of  the  different  groups  of  vertebrate  animals, 
is  most  interesting,  especially  when  prosecuted  with  a  view 
to  trace  them  all  back  to  one  fundamental  plan,  and  to  ob- 
serve the  modifications,  oftentimes  very  slight,  by  which  a 
very  simple  organ    is    adapted  to  every  variety  of   move- 
ment.    No  part  of  the  animal  structure  more  fully  illustrates 
the  unity  of  design,  or  the  skill  of  the  Intellect  which  has 
so  adapted  a  single  organ  to  such  multiplied  ends.     On  this 
account,  we  shall  illustrate  this  subject  somewhat  in  detail. 

171.  It  is  easy  to  see  that  the  wing  which  is  to  sustain 
the  bird  in  the  air  must  be  different  from  the  leg  of  the  stag, 
which  is  to  serve  for  running,  or  the  fins  of  the  fish  that 
swims.     But,  notwithstanding  their  dissimilarity,  the  wing  of 
the  bird,  the  leg  of  the  stag,  and  the  shoulder  fin  of  the  fish, 
may  still  be  traced  to  the  same  plan  of  structure  ;  and  if 
we  examine  their  skeletons,  we  find  the  same  fundamental 
parts.    In  order  to  show  this,  it  is  necessary  to  give  a  short  de- 
scription of  the  composition  of  the  arm  or  anterior  extremity. 

172.  The  anterior  member,  in  the  vertebrates,  is  invaria- 
b*y    composed  of   the    following   bones:    1.  The   shoulder- 
blade,  or  scapula,  (a,)  a  broad  and  flat  bone,  applied  upon 
the  b  )nes  of  the  trunk  •  2.  The  arm,  (Z»,)  formed  of  a  single 


OHGANS    OF    LOCOMOTION. 


S3 


-a 


long  cylindrical  bone,  the  humerus ;  3.  The  fore-arm  com- 
posed  of  two  long  bones,  the  radius,  (c,)  and  ulna,  (d,) 
which  are  often  fused  into  one  ;  4.  The  hand,  which  :.s 
composed  of  a  series  of  bones,  more 
or  less  numerous  in  different  classes, 
and  which  is  divided  into  three  parts, 
namely,  the  carpus,  or  wrist,  (e,)  the 
metacarpus,  or  palm,  (/,)  and  the  pha- 
langes, or  fingers,  (g.)  The  clavicle  or 
collar-bone,  (o,)  when  it  exists,  belongs 
also  to  the  anterior  member.  It  is  a 
bone  of  a  cylindrical  form,  fixed  as 
a  brace  between  the  breast-hone  and 
shou.der-blade.  Its  use  is  to  Veep  the 
shoulders  separated  ;  to  this  end,  we 
find  it  fully  developed  in  all  animals 
which  raise  the  limbs  from  the  sides,  as 
the  birds  and  the  bats.  On  the  other 
hano,  it  is  rudimentary,  or  entirely  want- 
ing in  animals  which  move  them  back- 
wards and  forwards  only,  as  with  most 
auadrupeds. 

,173.  The  following  outlines,  in  which  corresponding  bones 
are  indicated  by  the  same  letters,  will  give  an  idea  of  the 
modifications  which  these  bones  present  in  different  classes. 
In  the  arm  of  man,  (Fig.  34,)  the  shoulder-blade  is  fiat 
and  triangular  ;  the  bone  of  the  arm  is  cylindrical,  and  en- 
larged at  its  extremities  ;  the  bones  of  the  fore-arm  are 
somewhat  shorter  than  the  humerus,  but  more  slender ;  the 
hand  is  composed  of  the  following  pieces,  namely,  eight 
small  hones  of  the  carpus,  arranged  in  two  rows,  five  meta- 
carpal  bones,  which  are  elongated,  and  succeed  those  of  the 
wrist;  five  fingers  of  unequal  length,  one  of  which,  the 
thumb  is  opposed  to  the  four  others. 


Fig.  34. 


84 


ORGANS    OF    LOCOMOTION. 


174.  In  the  stag,  (Fig.  35,)  the   bones  of  the    fore-arm 
are  rather  longer  than  that  of  the  arm,  and   the  radius  no 
longer  turns  upon  the  ulna,  but  is  blended  with  it;  the  meta- 
rurpal,  or  cannon   bone,  is  greatly  developed  ;   and,  being 
quite  as  long  as  the  fore-arm,  it  is  apt  to  be  mistaken  for  it. 
The  fingers  are  reduced  to  two,  each  of  which  is  surrounded 
by  a  hoof,  at  its  extremity. 

175.  In  the  arm  of  the  lion,  (Fig.  36,)  the  arm  bone  is 


Fig.  36. 

stouter,  the  carpal  bones  are  less  numerous,  and  the  fingers 
are  short,  and  armed  with  strong,  retractile  claws.  In  the 
whale,  (Fig.  37,)  the  bones  of  the  arm  and  fore-arm  <are 
much  shortened,  and  very  massive ;  the  hand  is  broad,  the 
fingers  strong,  and  distant  from  each  other. 


Fig.  38.  S-     • 

In  the  bat,  the  thumb,  which  is  represented  by  a  small 
hook,  is  entirely  free,  (Fig.  38  ;)  but  the  fingers  are  elon- 
gated  in  a  disproportionate  manner,  and  the  skin  is  stretched 


ORGANS    OF    LOCOMOTION. 


85 


across  them,  so  as  to  serve  the  purpose  of  a  wing.  In  birds 
the  pigeon  for  example,  (Fig.  39,)  there  are  but  two  fingers 
which  are  soldered  together,  and  destitute  of  nails  ;  and  the 
thumb  is  rudimentary. 

176.  The  arm  of  the  turtle  (Fig.  40)  is  peculiar  in  having, 


Fig.  42. 

besides  the  shoulder-blade,  two  clavicles ;  the  arm-bone  is 
twisted  outwards,  as  well  as  the  bones  of  the  fore-arm,  so 
that  the  elbow,  instead  of  being  behind,  is  turned  forwa~ds; 
the  fingers  are  long,  and  widely  separated.  In  the  Sloth, 
(Fig.  41,)  the  bones  of  the  arm  and  fore-arm  are  very  greavly 
elongated,  and  at  the  same  time  very  slender ;  the  hand  is 
likewise  very  long,  and  the  fingers  are  terminated  by  enoi- 
mous  non-retractile  nails.  The  arm  of  the  Mole  (Fig.  42) 
is  still  more  extraordinary.  The  shoulder-blade,  which  is 
usually  a  broad  and  flat  bone,  becomes  very  narrow  ;  the 
arm-bone,  on  the  contrary,  is  contracted  so  much  as  to  seem 
nearly  square  ;  the  elbow  projects  backwards,  and^the  hand 
is  excessively  large  and  stout.  <^/r 

177.  In  fishes,  the  form  and  arrangement  of  Hke  bonos  is 
so  peculiar,  that  it  is  often  difficult  to  trace  their  correspond- 
ence to  all  the  parts  found  in  other  animals ;  nevertheless 
the  bones  of  the  fore-arm  are  readily  recognized.   In  the  Cod 
8 


86  ORGANS    OF    LOCOMOTION. 

(F  g.  43N  tlipro  are  two  flat  and  broad  bones,  one  of  which, 
the  ulna,  (rf,)  presents  a  long  point,  anteriorly.   The  bones  of 

c 


the  carpus  are  represented  by  four  nearly  square  little  bones. 
But  in  these  again  there  are  considerable  variations  in  dif- 
ferent fishes,  and  in  some  genera  they  are  much  more  irreg- 
ular in  form.  The  fingers  are  but  imperfectly  represented 
by  the  rays  of  the  fin,  (g,)  which  are  composed  of  an  infini- 
tude of  minute  bones,  articulated  with  each  other.  As  to 
the  humerus  and  shoulder,  their  analogies  are  variously  in- 
terpreted by  different  anatomists. 

178.  The  form  of  the  members  is  so  admirably  adapted  to 
the  special  offices  which  they  are  designed  to  perform,  that 
by  a  single  inspection  of  the  bones  of  the  arm,  as  repre- 
sented in  the  preceding  sketches,  one  might  infer  the  uses  to 
which  they  are  to  be  put.  The  arm  of  man,  with  its 
radius  turning  upon  its  ulna,  the  delicate  and  pliable  fingers, 
and  the  thumb  opposed  to  them,  bespeak  an  organ  for  the 
purpose  of  handling.  The  slender  and  long  arm  of  the 
sloth,  with  his  monstrous  claws,  would  be  extremely  incon- 
venient for  walking  on  the  ground,  but  appropriate  for  seizing 
upon  the  branches  of  the  trees,  on  which  these  animals  live. 
The  short  fingers,  armed  with  retractile  nails,  indicate  the 
lion,  at  first  glance,  to  be  a  carnivorous  animal.  The  arm 
of  the  stag,  with  his  very  long  cannon-bone,  and  that  of  the 
horse,  also,  with  its  solitary  finger,  enveloped  in  a  hoof,  are 
organs  especially  adapted  for  running.  The  very  slondcr 
and  greatly  elongated  fingers  of  the  bat  are  admirably  COD 


ORGANS    OF    LOCOMOTION.  87 

trived  for  the  spread  of  a  wing,  without  in  Creasing  the 
weight  of  the  body.  The  more  firm  and  solid  arm  of  the 
bird  indicates  a  more  sustained  flight.  The  short  arm  of  the 
whale,  with  his  spreading  fingers,  resembles  a  strong  oar. 
The  enormous  hand  of  the  mole,  with  its  long  elbow,  is  con* 
structed  for  the  difficult  and  prolonged  efforts  requisite  in  bur- 
rowing. The  twisted  arm  of  the  tortoise  can  be  applied  to  no 
other  movement  than  creeping.  And  finally,  the  arm  of  the 
fish,  completely  enveloped  in  the  mass  of  the  flesh,  presents, 
externally,  a  mere  delicate  balancer,  the  pectoral  fin. 

179.  The  posterior  members  are  identical  in  their  structure 
with   the    anterior   ones.      The   bones   of  which    they    are 
composed,  are,  1.  The  pelvis,  (Fig.  46,)  which  corresponds 
to  the  shoulder  blade  ;  2.  The  thigh  bone,  or  femur,  which 
is  a  single  bone,  like  the  humerus ;  3.  The  bones  of  the  leg, 
the  tibia  andjibula,  which,   like   the   radius  and  ulna,  some- 
times coalesce  into  one  bone ;  and    lastly,  the  bones  of  the 
foot,  which  are  divided,  like  those  of  the  hand,  into  three 
parts,  the  tarsus  or  ankle,  the  metatarsus  or  Instep,  and  the 
toes.     The  modifications  are   generally  les?  marked  than  in 
the  arm,  inasmuch  as  there  is  less  diversity  of  funttion  ;  for 
in  all  animals,  without  exception,  the   posterior  extremities 
are  used  exclusively  for  support  or  locomotion. 

180.  The  anterior  extremity  of  the  vejftebraies,  however 
varied  in  form,  whether  it  be  an 

arm,   a  wing,   or  a  fin,   is  thus 
shown  to  be  composed  of  essen- 
tially the  same   parts,  and  con- 
structed upon   the  same  general 
plan.   This  affinity  does  not   ex- 
tend to  the  invertebrates ;  for  al- 
though   in   many  instances  their        Fig.  44.       Fig.  45. 
limbs  bear  a  certain  resemblance  to  those  of  the  vertebrates, 
and  are  even  used  for  similar  purposes,  yet  they  have  no  real 


88  OF    STANDING    AND    PROGRESSION. 

affinity.  Thus  the  leg  of  an  insect,  (Fig.  44,)  and  tha 
of  a  lizard,  (Fig.  45  ;)  the  wing  of  a  butterfly  and  the 
wing  of  a  bat;  are  quite  similar  in  form,  position,  and  use, 
but  in  the  bat  and  the  lizard,  the  organ  has  an  internal  bony 
support,  which  is  a  part  of  the  skeleton  ;  while  the  leg  of 
the  insect  has  merely  a  homy  covering,  proceeding  from  one 
of  the  rings  of  the  body,  and  the  wing  of  the  butterfly  is 
merely  a  fold  of  the  skin,  showing  that  the  limbs  of  the 
Articulata  are  constructed  upon  a  different  plan,  (157.)  It 
is  by  ascertaining  and  regarding  these  real  affinities,  or 
the  fundamental  differences,  existing  between  similar  organs, 
that  the  true  natural  grouping  of  animals  is  to  be  attained. 

2.   Of  Standing,  and  the    Modes  of  Progression. 

181.  Standing,  or  the  natural  attitude   of  an  animal,  de- 
pends on  the  form  and  functions  of  the   limbs.     Most  of  the 
terrestrial  mammals,  and  the  reptiles,  both  of  which  employ 
all  four  limbs  in  walking,  have  the  back-bone  horizontal,  and 
resting  at  the  same  time  upon  both  the  anterior  and  poste- 
rior extremities.     Birds,  whose  anterior  limbs  are  intended 
for  a  purpose  very  different  from  the   posterior,  stand  upon 
the  latter,  when  at  rest,  although  the  back-bone  is  still  very 
nearly  horizontal.     Man  alone  is  designed  to  stand  upright, 
with  his  head  supported  on  the  summit  of  the  vertebral  col- 
umn.    Some  monkeys  can  rise  upon  the  hind  legs  into  the 
erect  posture ;  but  it  is  evidently  a  constrained  one,  and  not 
their  habitual  attitude. 

182.  That  an  animal  may  stand,   it  is  requisite  that  the 
limbs  should   be  so  disposed  that  the  centre  of  gravity,  in 
o'ther  words,  the  point  about  which  the  body  balances  itself, 
should  fall  within   the  space  included  by  the  feet.     If  the 
centre  of  gravity  is  outside   of  these  limits,  the  animal  falls 
to    he   side   to   which    the   centre   of  gravity  inclines.     On 
thifa    account,   the  albatross,  and  some  other  aquatic  birds 


OF    STANDING.  89 

which  have  the  feet  placed  very  far  back,  cannot  use  them 
for  walking. 

183.  The  more  numerous  and  the  more  widely  separated 
are  the  points  of  support,  the  firmer  an  animal  stands.  On 
this  account,  quadrupeds  are  less  liable  to  lose  their  balance 
than  birds.  If  an  animal  has  four  legs,  it  is  not  necessary 
that  the\  should  have  a  broad  base.  Thus  we  see  that 
mos:  quadrupeds  have  slender  legs,  touching  the  earth  by 
only  a  small  surface.  Broad  feet  would  interfere  with  each 
other,  and  only  increase  the  weight  of -the  limbs,  without 
adding  to  their  stability.  Birds  are  furnished  with  long  toes, 
which,  as  they  spread  out,  subserve  the  purpose  of  tripods. 
Moreover,  the  muscles  of  the  toes  are  so  disposed  that  the 
weight  of  the  bird  causes  them  to  grasp  firmly ;  hence  it 
is  enabled  to  sleep  standing  in  perfect  security  upon  the  roost, 
without  effort. 


Fig.  46. 

184.  In  quadrupeds,  the  joints  at  the  junction  of  the  limbs 
with  the  body  bend  freely  in  only  one  direction,  that  is,  to- 
wards the  centre  of  gravity ;  so  that  if  one  limb  yields,  the 
tendency  to  fall  is  counteracted  by  the  resistance  of  the 
limbs  at  the  other  extremity  of  the  body.  The  same  antag- 
onism is  observed  in  the  joints  of  the  separate  limbs,  which 
are  flexed  alternately  in  opposite  directions.  Thus  the  thigh 
bends  forwards,  and  the  leg  backwards  ;  whi'e  the  arm  bends 
8* 


90  MODES    OF    PROGRESSION. 

backwards,  and  the  fore-arm  forwards.  Different  terms  have 
been  employed  to  express  the  various  modes  of  progression, 
aecoid'ng  to  the  rapidity  or  the  succession  in  which  the 
limbs  are  advanced. 

185.  PROGRESSION  is  a  forward  movement  of  the  body, 
effected  by  successively  bending  and   extending  the  limbs. 
WALKING  is  the  ordinary  and   natural  gait,  and  other  paces 
are  only  occasionally  employed.     When  walking  is  accom- 
plished by  two  limbs   only,  as  in  man,  the  body  is  inclined 
forwards,  carrying  the  centre  of  gravity  in   that  direction ; 
and  while  one   leg  sustains  the  body,   the   other  is  thrown 
forwards  to  prevent  it  from  falling,  and  to  sustain  it  in  turn. 
For  this  reason,  walking  has  been  defined  to  be  a  continual 
falling  forwards,  continually  interrupted  by  the  projection  of 
the  legs. 

186.  The    throwing   forwards   of  the   leg,   which    would 
require  a  very  considerable  effort,  were  the  muscles  obliged 
to  sustain  the  weight  of  the  limbs  also,  is  facilitated  by  a  very 
peculiar  arrangement ;  that  is,  the  joints  are  perfectly  closed 
up  ;  so  that  the  external  pressure  of  the  atmosphere  is  suffi- 
cient of  itself  to  maintain  the  limbs  in  place,  without  the  as- 
sistance of  the  muscles.     This   may   be   proved   by  experi- 
ment.   If  we  cut  away  all  the  muscles  around  the  hip  joint,  the 
thigh  bone  still  adheres  firmly  to  the  pelvis,  but  separates  the 
moment  a  hole  is  pierced,  so  as  to  admit  air  into  the  socket. 

187.  In  ordinary  walking,  the  advancing  leg  touches  the 
ground  just  before  the  other  is  raised  ;  30  that  there  is  a 
moment  when  the  body  rests  on  both  limbs.     It  is  only  when 
the  speed   is   very   much  accelerated,  that  the  two  actions 
become  simultaneous.      The    walking   of  quadrupeds   is  a 
similar  process,  but  with  this  difference,  that  the  body  always 
rests  on  at  least  two  legs.     The  limbs  are  raised  in  a  deter- 
minate order,  usually  in  such  a  manner  that  the  hind-leg  of 
one  side  succeeds  th     fore-leg  of  the  opposite  side.     Some 


MODES    OF    PROGRESSION.  91 

animals,  as  the  giraffe,  the  lama,  and  the  bear,  raise  both 
legs  of  one  side  at  the  same  moment.  This  is  called  am- 
bling,  or  pacing. 

188.  RUNNING  consists  in  the  same  succession  of  motions 
as    walking,   so   accelerated   that   there    is   a    moment   be- 
tween two  steps  when  none  of  the  limbs  touch  the  ground. 
In  the  horse  and  dog,  and  in  most  mammals,  a  distinction  is 
made  between  the  walk,  the  trot,  the  canter,  and  the  gallop, 
all  of  which  have  different  positions  or  measures.     The  trot 
has  but  two  measures.     The  animal  raises  a  leg  on  each 
side,  in  a  cross  direction,  that  is  to  say,  the  right  fore-leg 
with  the    left  hind-leg,  and   so  on.     The   canter  has  three 
measures.     After  advancing  the  two  fore-legs,  one  after  the 
other,  the  animal  raises  and  brings  forward  the  two  hind-legs, 
simultaneously.      When  this    movement   is   greatly  urged, 
there  are  but  two   measures ;    the  fore-limbs  are  raised  to- 
gether as  well  as  the  hind-legs ;  it  is  then  termed  a  gallop. 

189.  LEAPING  consists  in  a  bending  of  all  the  limbs,  fol- 
lowed  by  a  sudden  extension  of  them,  which  throws  the 
body  forwards  with  so  much   force  as  to   raise  it  from  the 
ground,  for  an  instant,  to  strike  again  at  a  certain  distance  in 
advance.      For  this  purpose,  the    animal  always  crouches 
before  leaping.     Most  animals  make  only  an  occasional  use 
of  this  mode  of  progression,  when  some  obstacle  is  to  be 
surmounted  ;  but  in  a  few  instances,    this   is  the  habitual 
mode.     As  the  hind-legs  are  especially  used  in  leaping,  we 
observe  that  all  leaping  animals  have  the  posterior  members 
very  much  more  robust  than  the  anterior,  as  the  frog,  the 
kangaroo,  jerboa,  and  even  the  hare.     Leaping  is  also  com- 
mon  among  certain   birds,  especially  among  the  sparrows, 
the  thrushes,  &c.     Finally,  there  is  also  a  large  number  of 
leaping  insects,  sush  as  the  flea,  the  large  tribe  of  grass* 
hoppers   and  crickets,  in  which  we  find  that  pair  of  legs 
with  which  leaping  is  accomplished  much  more   developed 
than  the  others. 


92  MODES    OF    PROGRESSION. 

190.  CLIMBING   is   merely  walking  upon   an  inclined   or 
even  upright  surface.    It  is  usually  accomplished  by  means  of 
sharp  nails  ;    and   hence   many   carnivorous  animals  climb 
with  great  facility,  such   as  the  cat  tribe,  the  lizards  ;  and 
many  birds,  the  woodpecker,  for  instance.     Others  employ 
their  arms  for  this  purpose,  like  the   bears  when  they  clirnb 
a  tree  ;  or  their  hands,  and  even  their  tails,  like  the  mon- 
keys ;  'or  their  beaks,  like  the  parrots.  Lastly,  there  are  some 
whose  natural  mode  of  progression  is  climbing.     Such  are 
the  sloths,  with  their  arms  so  long,  that,  when  placed  upon 
the  ground,  they  move  very  awkwardly  ;  and  yet  their  struc 
ture  is  by  no  means  defective,  for  in  their  accustomed  move 
ments  upon  trees  they  can  use  their  limbs  with  very  great 
adroitness. 

191.  Most  quadrupeds   can  both  walk,  trot,  gallop,  and 
leap  ;  birds  walk  and  leap ;  lizards  neither  leap  nor  gallop, 
but  only  walk  and  run,  and  some  of  them  with  great  rapidity. 
No  insect  either  trots  or  gallops,  but  many  of  them  leap. 
Yet  their  leaping  is  not  always  the   effect  of  the  muscular 
force  of  their  legs,  as  with  the  flea   and   grasshopper ;  but 
some  of  them  leap  by  means  of  a  spring,  in  the  form  of  a 
hook,  attached  to  the  tail,   which  they    bend   beneath    the 
body,  and  which,  when  let  loose,   propels  them  to  a  great 
distance,  as  in  the  PodurellaB.     Still  others  leap  by  means  of 
a  spring,  attached  beneath  the  breast,  which  strikes  against 
the  abdomen  when  the  body  is  bent ;  as  the  spring-beetles, 
(Elaters.) 

192.  FLIGHT  is  accomplished  by  the  simultaneous  action 
of  the  two  anterior  limbs,  the  wings,  as  leaping  is  by  that  of 
the   two  hinder  limbs.     The  wings  being  expanded,  strike 
and  compress  the  air,  which  thus  becomes  a  support,  for  the 
mcment,  upon  which   the   bird    is   sustained.     But   as  this 
support  very  soon  yields,  owing  to  the  slight  density  of  the 
air,  it  follows  that  the  bird  must  make  the  greater  and  more 


MODES    OF    PROGRESSION.  93 

raf  id  efforts  to  compensate  for  this  disadvantage.  Kence  it 
requires  a  much  greater  expenditure  of  strength  to  fly  than 
to  walk ;  and,  therefore,  we  find  the  great  mass  of  muscles 
in  birds  concentrated  about  the  breast,  (Fig.  30.)  To  facili- 
tate its  prDgress,  the  bird,  after  each  flap  of  the  wings,  brings 
them  against  the  body,  so  as  to  present  as  little  surface  as 
possible  to  the  air  ;  for  a  still  further  diminution  of  resistance, 
all  birds  have  the  anterior  part  of  the  body  very  slender, 
Their  flight  would  be  much  more  difficult  if  they  had  large 
heads  and  short  necks. 

193.  Some  quadrupeds,  such  as   the  flying-squirrel  and 
Galeopithecus,  have  a  fold  of  the  skin  at  the  sides,  which 
may  be  extended  by  the  legs,  and  which  enables  them  to 
leap  from  branch  to  branch  with  more  security.     But  this 
is  not  flight,  properly  speaking,  since  none  of  the  peculiar 
operations  of  flight  are    performed.     There  are  also  some 
fishes,  whose  pectoral  fins  are  so  extended  as  to  enable  them 
to  dart  from  the  water,  and  sustain  themselves  for  a  consider- 
able time  in  the  air ;   and  hence  they  are  called  flying-fish. 
But  this  is  not  truly  flight. 

194.  SWIMMING  is  the  mode  of  locomotion  employed  by 
the  greater  part  of  the  aquatic  animals.     Most  animals  which 
live  in  the  water  swim  with  more  or  less  facility.     Swimming 
has  this  in  common  with  flight,  that  the  medium  in  which  it 
is  performed,  the  water,  becomes  also  the  support,  and  read 
ily  yields  also  to  the  impulse  of  the  fins.     Only,  as  water  is 
much  more  dense  than  air,  and  as  the  body  of  most  aquatic 
animals  is  of  very  nearly  the  same  specific  gravity  as  water, 
it  follows  that,  in  swimming,  very  little  effort  is  requisite  to 
keep  the  body  from  sinking.     The  whole  power  of  the  mus- 
cles is  consequently    employed   in   progression,  and    hence 
swimming  requires  vastly  less  muscular  force  than  flying. 

195.  Swimming  is  accomplished  by  means  of  various  or- 
gans designated  under  the  general  term,  fins,  although  in  an 


94  MODES    OF    PROGRESSION. 

anatomical  poiri:  of  view  these  may  represent  very  different 
parts.  In  the  Whales,  the  anterior  extremities  ar.  i  the  tail 
are  transformed  into  fins.  In  Fishes,  the  pectoral  fins,  which 
represent  the  arms,  and  the  ventral  fins,  which  represent  the 
legs,  are  employed  for  swimming,  but  they  are  not  the  prin- 
cipal organs ;  for  it  is  by  the  tail,  or  caudal  fin,  that  pro- 
gression is  principally  effected.  Hence  the  progression  of 
the  fish  is  precisely  that  of  a.  boat  under  the  sole  guidance 
of  the  sculling-oar.  In  the  same  manner  as  a  succes- 
sion of  strokes  alternately  right  and  left  propels  the  boat 
straight  forwards,  so  the  fish  advances  by  striking  alternately 
right  and  left.  To  advance  obliquely,  it  has  only  to  strike 
a  little  more  strongly  in  the  direction  opposite  to  that  which 
he  wishes  to  take.  The  Whales,  on  the  contrary,  swim  by 
striking  the  water  up  and  down ;  and  it  is  the  same  with  a 
few  fishes  also,  such  as  the  rays  and  the  soles.  The  air- 
bladder  facilitates  the  rising  and  sinking  of  the  fish,  by  ena- 
bling it  to  vary  the  specific  weight  of  the  body. 

196.  Most  land  animals  swim  with  more  or  less  ease,  by 
simply  employing  the  ordinary  motions  of  walking  or  leaping. 
Those  which  frequent  the  water,  like  thtr  beaver,  or  which 
feed  on  marine  animals,  as  the  otter  and  duck,  have  webbed 
feet ;  that  is  to  say,  the  fingers  are  united  by  a  membrane 
which,  when  expanded,  acts  as  a  paddle. 

197.  There  is  also  a  large  number  of  invertebrate  animals 
in  which  swimming  is  the   principal  or  the  only  mode  of 
progression.     Lobsters  swim  by  means  of  their  tail,  and,  like 
the  Whales,  strike  the  water  up  and  down.     Other  Crustacea 
have  a  pair  of  legs  fashioned  like  oars  ;  as  the  posterior  legs 
in  sea-crabs,  for  example..    Many  insects    likewise,  swim 
wilh  their  legs,  which  are  abundantly  fringed  with  hairs  to 
give  them  surface ;   as  the  little  water  boatmen,  (Gyrinus, 
Dytiscus,)  whose  mazy  dances  on  the  summer  streams  every 
one  must  have  observed.     The  cuttle-fish  uses  its  long  ten- 


MODES    OF    PROGRESSION.  95 

tacles  as  oars,  (Fig.  47 ;)  and  some  star-fishes  (Comatula, 
Euryale)  use  their  arms  with  great  adroitness,  (Fig.  151.) 
Finally,  there  are  some  insects  which  have  their  limbs  con- 
structed for  running  on  the  surface  of  water,  as  the  water- 
srulers,  (Ranatra,  Hydrometra.) 


Fig.  47. 

198.  A  large  number  of  animals  have  the  faculty  of  mov 
ing  both  in  the  air  and  on  land,  as  is  the  case  with  most  birds, 
and  a  great  proportion  of  insects.     Others  move  with  equal 
facility,  and  by  the  same  members,  on  land  and  in  water,  as 
some  of  the  aquatic  birds  and  most  of  the  reptiles,  which  latter 
have  even  received  the  name  Amphibia,  on  this  account. 
There  are  some  which  both  walk,  fly,  and  swim,  as  the  ducks 
and  water-hens ;    but  they  do  not  excel  in  either  mode  of 
progression. 

199.  However  different  the  movements  and   offices  pei- 
formed  by  the  limbs  may  appear  to  us,  according  to  the  ele- 
ment in  which  they  act,  we  see  that  they  are  none  the  less 
ihs  effect  of  the  same  mechanism.     The  contraction  of  the 
same  set  of  muscles  causes  the  leg  of  the  stag  to  bend  for 
laaping,  the  wing  of  the  bird  to  flap  in  the  air,  the  arm  of 
the  mole  to  excavat1   the  earth,  and  the  fin  of  the  whale  to 
strike  the  water.  , 


CHAPTER    SIXTH. 

NUTKITION. 

200.  THE  second  class  of  the  functions  of  animals  are 
those  which  relate  to  the  maintenance  of  life  and  the  per- 
petuation of  the  species ;  the  functions  of  vegetative  life,  (59.) 

201.  The  increase  of  the  volume  of  the  body  must  re 
quire  additional  materials.     There  is  also  an  incessant  waste 
of  particles  which,  having  become  unfit  for  further  use,  are 
carried  out  of  the  system.     Every  contraction  of  a  muscle 
exp&ftds  the  energy  of  some  particles,  whose  place  must  be 
supplied.     These   supplies   are  derived   from  every  natural 
source,  the  animal,  vegetabte,  and  even  the  mineral  king- 
doms ;  and  are  received  under  every  variety  of  solid,  liquid, 
and  gaseous  form.     Thus,  there  is  a  perpetual  interchange 
of  substance  between  the  animal  body  and  the  world  around. 
The  conversion  of  these  supplies  into  a  suitable  material,  its 
distribution  to  all   parts,  and  the  appropriation  of  it  to  the 
growth  and  sustenance  of  the  body,  is  called  NUTRITION  in 
the  widest  sense  of  that  term. 

202.  In  early  life,  during  the  period  of  growth,  the  amount 
of  substances  appropriated  is  greater  than  that  which  is  lost 
At  a  later  period,  when  growth  is  completed,  an  equilibrium 
between  the  matters  received  and  those  rejected  is  established. 
At  a  still  later  period,  the   equilibrium  is  again  disturbed, 
more  is  rejected  than  is  retained,  decrepitude  begins,  and  at 
last  the  organism  becomes  exhausted,  the  functions  cease,  and 
death  ensues. 

203.  The  solids  and  fluids  taken  into  the  body  as  food  are 


OF    DIGESTION.  9*7 

subjected  to  a  process  called  Digestion,  by  which  the  sclid 
portions  are  reduced  to  a  fluid  state  also,  the  nutritive  sepa 
rated  from  the  excrementitious,  and  the  whole  prepared  to 
become  blood,  bone,  muscle,  &c.  The  residue  is  afterwards 
expelled,  together  with  those  particles  of  the  body  which 
require  to  be  renewed,  and  those  which  have  been  derived 
from  the  blood  by  several  processes,  termed  Secretions. 
Matters  in  a  gaseous  form  are  also  received  and  expelled  with 
the  air  we  breathe,  by  a  process  called  Respiration.  The 
nutritive  fluids  are  conveyed  to  every  part  of  the  body  by 
currents,  usually  confined  in  vessels,  and  which,  as  they 
return,  bring  back  the  particles  which  are  to  be  either  reno- 
vated or  expelled.  This  circuit  is  what  is  termed  the  Circu- 
lation. The  function  of  Nutrition,  therefore,  combines  sev- 
eral distinct  processes. 

SECTION  I. 


OF    DIGESTION. 

'204.  Digestion,  or  the  process  by  which  the  nutritive  parts 
of  food  are  elaborated  and  pre- 
pared to  become  part  of  the  body, 
is  effected  in  certain  cavities,  the 
stomach  and  intestines,  or  alimen- 
tary canal.  This  canal  is  more  or 
less  complicated  in  the  various 
classes  of  animals  ;  but  there  is  no 
animal,  however  low  its  organiza- 
tion, without  it,  in  some  form,  (54.) 

205.  In  the  polypi,  the  digestive 
apparatus  is   limited   to  a   single 
cavity.  In  the  Sea  Anemone,  ( Ac- 
tinia,) for  example,  it  is  a  pouch,  (Fig   48,  b)  suspended  in 
9 


Fig.  48. 


98 


NUTRITION. 


Fig.  49. 


the  interior  of  the  body.  When  the  fooc  has  been  s  jffi /lently 
digested  there,  it  passes,  by  imbibition,  into  the  general  cav- 
ity of  the  body,  (c,)  which  is  filled  with  water,  and  mingling 
with  it,  flows  thence  into  all  parts  of  the  an- 
imal.  The  jelly-fishes,  (Medusse,)  and 
some  Worms,  have  a  distinct  stomach,  with 
appendages  branching  off  in  every  directior  , 
(Fig.  31,)  in  which  a  more  complete  elabo- 
ration takes  place.  The  little  worms  known 
by  the  name  of  Planaria,  present  a  striking 
example  of  these  ramifications  of  the  intes- 
tine, (Fig.  49,  e.)  But  here,  likewise,  the 
product  of  digestion  mingles  with  the  fluids 
of  the  cavity  of  the  body  which  surround 
the  intestine  (d)  and  its  branches,  and  cir- 
culation is  not  yet  distinct  from  diges- 
tion. 

206.  As  we  rise  in  the  scale  of  animals,  the  functions 
concerned  in  nutrition  become  more  and  more  distinct  from 
each  other.     Digestion  and  circulation,  no  longer  confounded, 
are  accomplished  separately,  in  distinct  cavities.     The  most 
important  organs  concerned  in  di- 
gestion are  the  stomach,  and  the 
small  and  large   intestine.     The 
first  indications  of  such  a  distinc- 
tion are  perceived  in  the  higher 
Radiata,"  such  as  the  sea-urchins, 
(Fig.  50,)  in  which  the  stomach  (s) 
is  broader  than  either  extremity  of 
the  intestine.    The  dimensions  and 
Fig-  50.  form  of  the  cavities  of  the  intestine 

very  considerably,  according  to  the  mode  of  life  of  the  ani- 
mal;  but  the  special  functions  assigned  to  them  are  invaria- 
ble ;  aria  the  three  principal  cavities  succeed  each  other,  in 


OF    DIGESTION. 


99 


every.. animal  where  they  are  found,  in  an  i:. variable  order: 
first,  the  stomach,  (s,)  then  the  intestine,  which  is  small  al 
first,  but  often  enlarged 
towards  its  termination. 
This  arrangement  may 
be  seen  by  the  follow- 
ing diagrams  from  a  bee- 
tle and  a  land  mollusk, 
where  the  same  letters 
indicate  corresponding 
parts,  (Figs.  51,  52.) 

207.  From  the  mouth, 
(m,)  the  food  passes  into 
the  stomach  through  a 
narrow  tube  in  the  neck, 
called  the  oesophagus  -or 
gullet,  (o.)  This  is  not  FiS-61-  Fis-52- 

always  a  direct  passage  of  uniform  size  ;  but  there  is  some- 
times a  pouch,  the  crop,  (c,)  into  which  the  food  is  first  intro- 
duced, and  which  sometimes  acquires  considerable  dimen- 
sions, especially  in  birds,  and  in  some  insects  and  mollusks. 
(Fig.  51.)  In  the  stomach,  the  true  digestive  process  is  be- 
gun. The  food  no  sooner  arrives  there  than  changes  com 
mence,  under  the  influence  of  a  peculiar  fluid  called  the  gas- 
trie  juice,  which  is  secreted  by  glands  lining  the  interior  of 
the  stomach.  The  digestive  action  is  sometimes  aided  by  the 
movements  of  the  stomach  itself,  which,  by  its  strong  contrac- 
tions, triturates  the  food.  This  is  especially  the  case  in  the 
gizzard  of  some  birds,  which,  in  the  hens  and  ducks,  for  in- 
stance, is  a  powerful  muscular  organ.  In  some  of  the  Crus- 
tacea and  Mollusks,  as  the  Lobster  and  Aplysia,  there  are 
even  solid  organs  for  breaking  down  the  food  within  the 
stomach  itself. 

208    The  result  of  this  process  is  the  reduction  of  the  food 


100  NUTRITION. 

.o  a  pulpy  fluid  called  chyme,  which  varies  in  its>  nature  with 
ths  food.  Hen.ce  the  function  of  the  stomach  has  been 
named  chymification.  With  this,  the  function  of  digestion  is 
complete  in  many  of  the  lower  animals,  and  chyme  is  circu- 
lated throughout  the  body  ;  this  is  the  case  in  Polypi  and  Jelly- 
fishes,  and  some  Worms  and  Mollusks.  In  other  animals, 
however,  the  chyme  thus  formed  is  transferred  to  the  intes- 
tine, by  a  peculiar  movement,  like  that  of  a  worm  in  creep- 
ing, which  has  accordingly  received  the  name  of  vermicular 
or  peristaltic  motion. 

209.  The   form  of  the  small  intestine  (i)  is  less  variable 
than  that  of  the  stomach.     It  is  a  narrow  tube,  with  thin  walls, 
coiled  in  various   directions  in  the  vertebrate  animals,  but 
more  simple  in  the  invertebrates,  especially  the  insects.     Its 
length  varies,  according  to  the  nature  of  the  food,  being  in 
general  longer  in  herbivorous  than  in  carnivorous  animals. 
In  this  portion  of  the  canal,  the  aliment  undergoes  its  com- 
plete elaboration,  through  the  agency  of  certain  juices  which 
here  mingle  with  the  chyme,  such  as  the  bile  secreted  by  the 
liver,  and   the   pancreatic  juice,  secreted   by  the  pancreas. 
The  res  cut  of  this  elaboration  is  to  produce  a  complete  sepa 
ration  of  the  truly  nutritious  parts,  in  the  form  of  a  milky 
^quid  called  chyle.     The  process  is  called  chylification ;  and 
there  are  great  numbers  of  animals,  such   as  the  Insects, 
Crabs,  and  Lobsters,  some  Worms,  and  most  of  the  Mollusks, 
in  which  the  product  of  digestion  is  not  further  modified  by 
respiration,  but  circulates  throughout  the  body  as  chyle. 

210.  The  chyle  is  composed  of  minute,  colorless  globules 

of  a  somewhat  flattened  form,  (Fig.  53.)  In 
the  higher  animals,  the  Vertebrates,  it  is  taken 
up  and  carried  into  the  blood  by  means  of  very 
minute  vessels,  called  lymphatic .  vessels  or 
lacteals,  which  are  distributed  every  where  in 
the  walls  of  the  intestine,  and  communicate 


OF    DIGESTION.  101 

with  the  veins,  forming  also  in  their  course  several  glandular 

masses,  as  seen  in  a  portion  of  intestine  connected  with  a  vein 

in  Fig.  54  •  and  it  is  not  until  thus 

taken   up   and   mingled  with  the 

circulating  blood,  that  any  of  our 

food  really  becomes  a  part  of  the 

living  body.     Thus  freed  of  the 

nutritive  portion  of  the  food,  the 

residue  of  the  product  of  digestion 

passes  on  to  the  large  intestine, 

from  whence  it  is  expelled  in  the 

form  of  excrement.  Flg'  54< 

211.  The  organs  above  described  constitute  the  most  es 
sential  for  the  process  of  digestion,  and  are  found  more  or  less 
developed  in  all  but  some  of  the  radiated  animals;  but  there 
are,  in  the  higher  animals,  several  additional  ones  for  aiding 
in  the  reduction  of  the  food  to  chyme  and  chyle,  which  render 
their  digestive  apparatus  quite  complicated.   In  the  first  place, 
hard  parts,  of  a  horny  or  bony  texture,  are  usually  placed  about 
the  mouth  of  those  animals  that  feed  on  solid  substances,  which 
serve  for  cutting  or  bruising  the  food  into  small  fragments 
before  it  is  swallowed  ;  and,  in  many  of  the  lower  animals, 
these  organs  are  the  only  hard  portions  of  the  body.     Thia 
process  of  subdividing  or  chewing  the  food  is  termed  masti> 
cation. 

212.  Beginning  with  the  Radiata,  we  find  the  apparatus 
for  mastication  partaking  of  the  star-like  arrangment  which 
characterizes  those  animals.      Thus   in  Scutella,  (Fig.  55,) 
we  have  a  pentagon  composed  of  five  triangular  jaws,  con- 
verging at  their  summits  towards  a  central  aperture  \\hich 
corresponds  to  the  mouth,  each  one  bearing  a  cutting  plate  or 
tooth,  like  a  knife-blade,  fitted  by  one  edge  into  a  cleft.     The 
five  jaws  move  towards  the  centre,  and  pierce  or  cut  the  ob- 
jects which  come  between  them.     In  some  of  the  sea-urchins 

9* 


102  NUTRITION. 

(Echinus,)  this  apparatus,  which  has  been  called  Aristotle's 


Fig.  55. 


Fig.  56. 


lantern,  (Fig.t56,)  consists  of  numerous  pieces,  and  is  much 
more  complicated.  Still,  the  five  fundamental  pieces  or  jaws, 
each  of  them  bearing  a  tooth  at  its  point,  may  be  recognized, 
as  in  Scutella ;  only  instead  oT  being  placed  horizontally, 
they  form  an  inverted  pyramid. 

213.    Among  the  Mollusks,  a  few,  like  the  cuttle-fishes, 
have  solid  jaws  or  beaks  closely  resembling 
the   beak  of  a  parrot,  (Fig. 
57,)    which    move    up    and 
down   as   in   birds.      But   a 
much    larger    number    rasp 
their  food  by  means  of  a  flat 
Fig.  57.  blade  coiled  up  like  a  watch-  Fig.  58. 

spring,  the  surface  of  which  is  covered  with  innumerable 
minute  tooth-like  points  of  a  horny  consistence,  as  seen  in  a 
highly  magnified  portion -of  the  so-called  tongue  of  Natica, 
(Fig.  58,  a,)  which,  however,  is  only  a  modification  of  the 
beaks  of  cuttle-fishes. 

214.  The  Articulata  are  remarkable,  as 
a  class,  for  the  diversity  and  complication 
of  their  a^  paratus  for  taking  and  dividing 
their  food.  In  some  marine  worms,  Nereis 
for  exarr  pie,  the  jaws  consist  of  a  pair  of 
Fig.  59.  curved,  horny  instruments,  lodged  in  ~8 

sheath,  (Fig.  59  )     In  spiders,  these  jaws  are  external,  and 


OF    DIGESTION. 


103 


sometimes  mounted  on  long,  joined  stems.  Insects  which 
masticate  their  food  have,  for  the  most  part,  at  least  two  pairs 
of  horny  jaws,  (Figs.  60,  61,  m,j?)  besides  several. additional 
pieces  which  serve  for  seizing  and  holding  their  food. 
Those  which  live  on  the  fluids  which  they  extract  either  from 
plants  or  from  other  animals,  have  the  masticatory  organs 
transformed  into  a  trunk  or  tube  for  that  purpose.  This 
trunk  is  sometimes  rolled  up  in  a  spiral  manner,  as  in  the 
butterfly,  (Fig.  64;)  or  it  is  stiff",  and  folded  beneath  the 


t- 

Fig.  60.  Fig.  61.  Fig.  62.     Fig.  63.  Fig.  64. 

chest,  as  in  the  squash-bugs,  (Fig.  62,)  containing  several 
piercers  of  extreme  delicacy,  (Fig.  63,)  adapted  to  penetrate 
the  skin  of  animals  or  other  objects  whose  juices  they  extract ; 
or  they  are  prolonged  so  as  to  shield  the  tongue  when  thrust 
out  in  search  of  food,  as  in  the  bees,  (Fig.  61,  t.)  The  crabs 
have  their  anterior  feet  transformed  into  a  kind  of  jaws,  and 
several  other  pairs  of  articulated  appendages  performing  ex- 


Fig.  65.  Fig.  66. 

cljsively  masticatory  functions.  Even  in  the  microscopic 
Rotifers,  we  find  very  complicated  jaws,  as  seen  in  a  Brachi 
onus,  (Fig.  65,)  and  'still  more  magnified  in  Fig.  66.  But 


104 


NUTRITION. 


amidst  this  diversity  of  ^paratus,  there  is  one  thing  ,\  nich 
characterizes  all  the  Articulata,  namelv,  the  jaws  always 
move  sideways ;  while  those  of  the  Vertebrates  and  Mollusks 
move  up  and  down,  and  those  of  the  Radiata  concentrically. 

21 5.  In  the  Vertebrates,  the  jaws  form  a  part  of  the  bony 

skeleton.  In  most  of  them  the 
lower  jaw  only  is  movable,  and 
is  brought  up  against  the  upper 
jaw  by  means  of  very  strong  mus- 
cles, the  temporal  and  masseter 
Fig.  67.  muscles,  (Fig.  67,  t,  m,)  which 

perform  the  principal  motions  requisite  for  seizing  and  mas- 
ticating food. 

216.  The  jaws   are    usually  armed    with    solid     cutting 

instruments,  the  TEETH,  or  else  are 
enveloped  in  a  horny  covering,  the 
beak,  as  in  the  birds  and  tortoises, 
(Fig.  68.)  In  some  of  the  whales, 
the  true  teeth  remain  concealed  in  the 
jaw-bone,  and  we  have  instead  a  range 
of  long,  flexible,  horny  plates  or  fans,  fringed  at  the  margin, 
which  serve  as  strainers  to  separate  the  minute  marine  ani- 
mals on  which  they  feed 
from  the  water  drawn  in 
with. them,  (Fig,  69.) 
A  few  are  entirely  des- 
titute of  teeth,  as  the 
ant-eater,  (Fig.  70.) 

217.    Though  all  the 
vertebrates  possess  jaws. 

Fig.  69.  it  must  not  be  in/erred 

that  they  all  chew  their  food.  Many  swallow  their  prey 
whole ;  as  most  birds,  tortoises,  and  whales.  Even  many  of 
chose  which  are  furnished  with  teeth  do  not  masticate  their 


Fig.  68. 


Of    DIGESTION. 


105 


food,  some  using  them  merely  for  seizing  and  securing  their 
prey,  as  the  lizards,  frogs,  crocodiles,  and  the  great  majority 
of  fishes.  In  such  animals,  the  teeth  are  nearly  all  alike  in 
form  and  structure,  as  for  instance,  in  the  alligator,  (Fig.  71,) 
Ihe  porpoises,  and  many  fishes.  A  few  of  the  latter,  some  of 


Fig.  71.  Fig.  72. 

the  Rays,  for  example,  have  a  sort  of  bony  pavement,  (Fig. 
72,)  composed  of  a  peculiar  kind  of  teeth,  with  which  they 
crush  the  shells  of  the  mollusks  and  crabs  on  which  they 
feed. 

218.  The  Mammals,  however,  are  almost  the  only  verte 
brates  which  can  properly  be  said  to  masticate  their  food 
Their  teeth  are  well 
developed,  and  pre- 
sent great  diversity 
in  form,  arrangement 
and  iflode  of  inser- 
tion. Three  kinds 
of  teeth  are  usually 
distinguished  in  most 
of  these  animals, 
whatever  may  be  .  Fig.  73. 

their  mode  of  life;  nar'ely,  the  cutting  teeth,  incisors;  the 


a 


106  NUTRITION. 

tusks  or  carnivorous  teeth,  canines ;  and  the  grinders,  molars 
(Fig.  73.)  The  incisdrs  (a)  occupy  the  front  of  the  mouth, 
the  upper  ones  being  set  in  the  intermaxillary  bones  ;  they 
are  the  most  simple  and  the  least  varied,  have  generally 
a  thin  cutting  summit,  and  are  employed  almost  exclusively 
for  seizing  food,  except  in  the  elephant,  in  which  they  assume 
the  form  of  large  tusks.  The  canines  (b)  are  comcal,  mc:e 
elongated  than  the  others,  more  or  less  curved,  and  only  two 
in  each  jaw.  They  have  but  a  single  root,  like  the  incisors, 
and  in  the  carnivora  become  very  formidable  weapons.  In 
the  herbivora,  they  are  wanting,  or  when  existing  they  are 
usually  so  enlarged  and  modified  as  also  to  become  powerful 
organs  of  offence  and  defence,  although  useless  for  mastica- 
tion ;  as  in  the  baljyroussa,  &c.  The  molars  (c)  are  the  most 
important  for  indicating  the  habits  and  internal  structure  of 
the  animal ;  they  are,  at  the  same  time,  most  varied  in 
shape.  Among  them  we  find  every  transition,  from  those  of 
a  sharp  and  pointed  form,  as  in  the  cat  tribe,  to  those  with 
broad  and  level  summits,  as  in  the  ruminants  and  rodents. 
Still,  when  most  diversified  in  the  same  animal,  they  have 
one  character  in  common,  their  roots  being  never  simple, 
but  double  or  triple,  a  peculiarity  which  not  only  fixes  them 
more  firmly,  but  prevents  them  from  being  driven  into  the 
jaw  in  the  efforts  of  mastication. 

219.  The  harmony  of  organs  already  spoken  of  (22-24) 
is  illustrated,  in  a  most  striking  manner,  by  the  study  of  the 
teeth  of  the  mammals,  aH  especially  of  their  molar  teeth. 
So  constantly  do  they  correspond  with  the  structure  of  the 
other  parts  of  the  body,  that  a  single  molar  is  sufficient  not 
only  to  indicate  the  mode  of  life  of  the  animal  to  which  i 
belongs  and  show  whether  it  feeds  on  flesh  or  vegetables,  or 
bo'  i,  bit  also  to  determine  the  particular  group  to  which  it  is 
related.  Thus,  those  beasts  of  prey  which  feed  on  insects, 
and  which  on  that  account  have  been  called  Insectivora,  such 


OF    DIGESTION.  107 

* 

as  the  moles  and  bats,  have  the  molars  terminated  by  several 


Fig.  76.  Fig.  75. 

sharp,  conical  points,  (Fig.  74,)  so  arranged  that  the  eleva- 
tions of  one  tooth  fit  exactly  into  the  depressions  of  the  tooth 
opposite  to  it.  In  the  true  Carnivora,  (Fig.  75,)  on  the  con- 
trary, the  molars  are  compressed  laterally,  so  as  to  have 
sharp,  cutting  edges,  as  in  the  bats ;  and  they-  shut  by  the 
side  of  each  other,  like  the  blades  of  scissors,  thereby  di 
viding  the  food  with  great  facility. 

220.  The  same  adaptation  is  observed  in  the  teeth  of  her- 
bivorous  animals.     Those  which  chew  the  cud,  (ruminants,) 
many  of  the  thick-skinned  animals,  (pachydermata,)  like  the 
elephant,  and  some  of  the  gnawers,  (rodentia,)  like  the  hare, 
(Fig.  76,)  have  the  summits  of  the  molars  flat,  like  mill-stones, 
with  more  or  less  prominent  ridges,  for  grinding  the  grass 
and  leaves  on  which  they  subsist.     Finally,  the  omnivora, 
those  which  feed  on  both  flesh  and  fruit,  like  man  and  the 
monkeys,  have  the   molars  terminating  in  several  rounded 
tubercles,  being  thus  adapted  to  the  mixed  nature  of  their 
food. 

221.  Again,  the  mode  in  which  the  molars  are  combined 
with  the  canines  and  incisors  furnishes  excellent  means  of 

"characterizing  families  and  genera.  Even  the  internal  struc- 
ture of  the  teeth  is  so  peculiar  in  each  group  of  animals,  and 
yet  subject  to  such  invariable  rules,  that  it  is  possible  to 
determine  with  precision  the  general  structure  of  an  animal 


108  NUTRITION. 

merely  by  investigating  the  fragment  of  a  tooth  under  a  mi 
croscope. 

222.  Another  process,  subsidiary  to   digestion,   is  called 
tnsalivation.     Animals    which     masticate    their    food    ha\e 
glands,  in  the  neighborhood  of  the  mouth,  which  secrete  a 
fluid  called  saliva.     This  fluid  mingles  with  the  food  as  it  is 
chewed,  and  "prepares  it  also  to  be  more  readily  swallowed. 
The  salivary  glands  are  generally  wanting,  or  rudimentary. 
or  otherwise  modified,  in  animals  which  swallow  their  food 
without  mastication.     After  it  has  been  masticated  and  min- 
gled with  saliva,  it  is  moved  backwards  by  the  tongue,  and 
passes  down  through  the  oesophagus,  into  the  stomach.     This 
act  is  called  deglutition  or  swallowing. 

223.  The  wisdom  and   skill  of  the  Creator  is  strikingly 
illustrated  in.  the  means  he  has  afforded  to  every  creature  for 
securing   the    means    for  subsistence.     Some  animals  ha\e 
no  ability  to  move  from  place  to  place,  but  are  fixed  to  the 
soil ;  as  the  oyster,  the  polyp,  &c.     These  are  dependent  for 
subsistence  upon  such  food  as  may  stray  or  float  near,  and 
they  have  the   means  of  securing  it  when   it  comes  within 
their  reach.     The  oyster  closes  its  shell,  and  thus  entraps  its 
prey  ;  the   polyp   has  flexible  arms,  (Fig.  77,)  capable  of 

great    extension,    which   it   throws   instantly 
„  v          around  any  minute  animal  that  comes  in  con- 
''    -^"^         tact  with  it.  The  cuttle-fish,  also,  has  elongated 
arms  about  the  mouth,  furnished  with  ranges 
of  suckers,   by  which    it   secures   its   prey, 
(Fig.  47.) 

224.  Some  are  provided  with  instruments 
Fig.  77  for  extracting  food  from  places  which  would 

be  otherwise  inaccessible.  Some  of  the  mollusks,  with  their 
rasp-like  tongue,  (Fig.  58,)  perforate  the  shells  of  other  ani 
mals,  and  thus  reach  and  extract  the  inhabitant.  Insects 
have  vario  is  piercers,  suckers,  or  a  protractile  tongue  for  the 


OF    DIGESTION.  109 

same  purpose,  (Figs.  61-64.)  Many  Annelides,  the  leeches 
for  example,  have  a  sucker,  which  enables  them  to  produce 
a  vacuum,  and  thereby  draw  out  blood  from  the  perforations 
they  make  in  other  animals.  Many  microscopic  animals  are 
provided  with  hairs  or  cilia  around  the  mouth,  (Fig.  65,) 
which  by  their  incessant  motion  produce  currents  that  bring 
within  reach  the  still  more  minute  creatures  or  particles  CD 
which  they  feed. 

225.  Among  the  Vertebrata,  the  herbivora  generally  em- 
ploy their  lips  or  their  tongue,  or  both  together,  for  seizing 
the  grass  or  leaves  they  feed  upon.     The  carnivora  use  their 
jaws,  teeth,  and  especially  their  claws,  which  are  long,  sharp 
even  movable,  and  admirably  adapted  for  the  purpose.     The 
woodpeckers   have   long,  bony  tongues,  barbed   at  the  tip, 
with  which  they  draw  out  insects  from  deep  holes  and  crevi- 
ces in  the  bark  of  trees.     Some  reptiles  also  use  their  tongue 
to  take  their  prey.     Thus,  the  chameleon  obtains  flies  at  a 
distance  of  three  or  four  inches,  by  darting  out  his  tongue, 
the  enlarged  end  of  which  is  covered  with  a  glutinous  sub- 
stance to  which   they  adhere.     The   elephant,  whose   tusks 
and  short  neck  prevent  him  from  bringing  his  mouth  to  the 
ground,  has  the  nose  prolonged  into  a  trunk,  which  he  uses 
with  great  dexterity  for  bringing  food  and  drink  to  his  mouth, 
Doubtless  the  mastodon,  once  so  abundant  in  this  country, 
was  fuinished  with  a  similar  organ.     Man  and  the  monkeys 
employ  the  hand  exclusively,  for  prehension. 

226.  Some  animals  drink  by  suction,  like  the  ox,  others 
by  lapping,  like  the  dog.     Birds  simply  fil    the  beak  with 
water,  then,  raising  the  head,  allow  it   to  run  down  into  the 
nrop.      It    is  difficult  to  say    how  far   aquatic    animals    re- 
quire water  with  their  food  ;  it  seems,  however,  impossible 
tha1"  they  should  swallow  their  prey  without  introducing  n$ 
the  same   time   some  water  into  their  stomach.     Of  many 
among  the   lowest   animals,  such  as  the  Polyps    it  is  well 

10 


110  OF    DIGESTION. 

known  that  they  frequently  fill  the  whole  cavity  of  their  body 
with  water,  through  the  mouth,  the  tentacles,  and  poiea 
upon  the  sides,  and  empty  it  at  intervals  through  the  same 
openings.  And  thus  the  aquatic  mollusks  introduce  water 
into  special  cavities  of  the  body,  or  between  their  tissues, 
through  various  openings,  while  others  pump  it  into  their 
blood  vessels,  through  pores  at  the  surface  of  their  body. 
This  is  the  case  with  most  fishes. 

226  a.  Besides  the  more  conspicuous  organs  above  de- 
scribed, there  are  among  the  lower  animals  various  micro- 
scopic apparatus  for  securing  their  prey.  The  lassos  of  polypi 
have  been  already  mentioned  incidentally,  (223.)  They  are 
minute  cells,  each  containing  a  thin  thread  coiled  up  m  its 
cavity,  which  may  be  thrown  out  by  inversion,  and  extend  to 
a  considerable  length  beyond  the  sac  to  which  it  is  at 
tached.  Such  lassos  are  grouped  in  clusters  upon  the  ten- 
tacles, or  scattered  upon  the  sides  of  the  Actinia  and  of 
most  polypi.  They  occur  also  in  similar  clusters  upon  the 
tentacles  and  the  disk  of  jelly-fishes.  The  nettling  sensa- 
cion  produced  by  the  contact  of  many  of  these  animals  is 
undoubtedly  owing  to  the  lasso  cells.  Upon  most  of  the 
smaller  animals,  they  act  as  a  sudden,  deadly  poison.  In 
Echinoderms,  such  as  star-fishes,  and  sea-urchins,  we  find 
other  microscopic  organs  in  the  form  of  clasps,  placed  upon 
a  movable  stalk.  The  clasps,  which  may  open  and  shut  al- 
ternately, are  composed  of  serrated  or  hooked  branches, 
generally  three  in  number,  closing  concentrically  upon  each 
other.  With  these  weapons^  star-fishes  not  more  than  two 
inches  in  diameter  may  seize  and  retain  shr  mps  of  half 
that  length,  notwithstanding  their  efforts  to  dise.«tf  igle  them- 
selves. 


CHAPTER    SEVENTH. 


CF  THE  BLOOD  AND  CIRCULATION. 


227.  THE  nutritive  portions  of  the   food   are  poured  into 
the  general  mass  of  fluid  which   pervades  every  part  of  tin- 
body,  out  of  which   every  tissue  is  originally  constructed, 
and  from  time  to  time  renewed.     This  fluid,  in  the  general 
acceptation  of  the  term,  is  called  blood  ;  but  it  differs  greatly 
in  its  essential  constitution   in   the   different  groups  of  the 
Animal    Kingdom.     In    polypi    and    medusai,    it  is    merely 
chyme,  (208 ;)  in  most  mollusks  and  articulates  it  is  chyle, 
(209  ;)  but  in  vertebrates  it  is  more  highly  organized,  and 
constitutes  what  is  properly  called  BLOOD. 

228.  The  BLOOD,  when  examined  by  the  microscope,  is 
found  to  consist  of  a  transparent-fluid,  the  serum,  consisting 
chiefly  of  albumen,  fibrin,  and  water,  in   which  float  many 
rounded,  somewhat  compressed  bodies,  called  blood  disks 


Fig.  78.  Fig.  79.  Fig.  80.  Fig.  81. 

These  vary  in  number  with  the   natural  heat  of  the  animal 
*ro:n  which  the  blood  is  taken.     Thus,   they  are   more  nu 


112  OF    THE    BLOOD 

merous  in  birds  than  in  mammals,  and  more  abundant  in  the 
latter  than  in  fishes.  In  man  and  other  mammals  they  are 
very  small  and  nearly  circular,  (Fig.  78  ;)  they  are'  some- 
what larger,  and  of  an  oval  form,  in  birds  and  fisiies,  (Figs 
79,  81  ;)  and  still  larger  in  reptiles,  (Fig.  80.) 

229.  The  color  of  the  blood   in  the  vertebrates  is  bright 
red  ;  but  in  some  invertebrates,  as  the  crabs  and  mollusks, 
the  nutritive  fluid  is  nearly  or  quite  colorless ;  while  in  the 
worms  and  some  echinoderms,  it  is  variously  colored  yellow, 
orange,  red,  violet,  lilac,  and  even  green. 

230.  The  presence  of  this  fluid  in  every  part  of  the  body 
is  one  of  the  essential   conditions  of  animal  life.     A   per- 
petual current  flows  from  the  digestive  organs  towards  the 
remotest  parts  of  the  surface  ;  and  such  portions  as  are  not 
required  for  nutriment  and  secretions  return  to  the  centre  of 
circulation,  mingled  with  fluids  which  need  to  be  assimilated 
to  the  blood,  and  with  particles  of  the  body  which  are  to  be 
expelled,  or,  before  returning  to  the  heart,  are  distributed  in 
the  Hv3r.     The  blood  is  kept  in  an  incessant  CIRCULATION 
for  this  purpose. 

231.  In  the  lowest  animals,  such  as  the  polypi,  the  nutri- 
tive fluid  is  simply  the  product  of  digestion  (chyme)  mingled 
with  water  in  the  common  cavity  of  the  viscera,  with  which 
it  comes  in  immediate  contact,  as  well  as  with  the  whole 
interior  of  the   body.     In  the  jelly-fishes,  which  occupy  a 
somewhat  higher  rank,  a  similar  liquid  is  distributed  by  pro- 
longations of  the   principal  cavity  to  different  parts  of  the 
body,  (Fig.  31.)     Currents  are  produced  in  these,  partly  by 
the  .general  movements  of  the  animal,  and  partly  by  means 
of  the    incessant  vibrations  of    microscopic    fringes,    called 
vibratile  cilia,  which  overspread  the  interior.     In  most  of 
the  mollusks  and  articulates,   the   blood   (chyle)  is  also  'n 
immediate  contact  with  the  viscera,  water  being  mixe<i  with 
it  in  mollusks ;  the  vessels,  if  there  are  any,  not  forming  a 


AND    CIRCULATION. 


113 


complete  circuit,  but  emptying  into  various  cav  ties  which 
interrupt  their  course. 

232.  In  animals  of  still  higher  organization,  as  the  verte- 
brates, we  find  the  vital  fluid  enclosed  in  an  appropriate  sei 
of  vessels,  by  which  it  is  successively  conveyed  throughout 
the  system  to  supply  nutriment  and  secretions,  and  to  the 
respiratory  organs,  where    it  absorbs  oxygen,  or,  in  other 
words,  becom  3s  oxygenated. 

233.  The  vassels  in  which  the  blood  circulates  are  of  two 
kinds :   1.  The  arteries,  of  a  firm,  elastic  structure,  which 
may  be  distended  or  contracted,  according  to  the  volume  of 
their  contents,  and  which  convey  the  blood  from  the  centre 
towards  the    surface,  distributing  it  to  every  point  of  the 
body.     2.  The   veins,   of  a   thin,    membranous 
structure,   furnished   within   with    valves,    (Fig. 

82,  v,)  which  aid  in  sustaining  the  column  of 
blood,  only  allowing  it  to  flow  from  the  peri- 
phery towards  the  centre.  The  arteries  con- 
stantly subdivide  into  smaller  and  smaller 
branches ;  while  the  veins  commence  in  minute 
twigs,  and  are  gathered  into  branches  and  larger 
trunks,  to  unite  finally  into  a  few  stems,  near  the 
centre  of  circulation. 

234.  The  extremities  of  the  arteries  and  veins  are  con- 
nected by  a  net-work  of  extremely 

delicate  vessels,  called  capillary  ves- 
sels, (Fig.  83.)  They  pervade  every 
portion  of  the  body,  so  that  almost 
no  point  can  be  pricked  without 
drawing  blood.  Their  office  is  to 
distribute  the  nutritive  fluid  to  the 
organic  cells,  where  all  the  important  processes  of  nutrition 
are  performed,  such  as  the  alimentation  and  growth  of  all 
organs  and  tissues,  the  elaboration  of  bile,  milk,  saliva,  anc 
10* 


Fig.  82. 


Fig.  83. 


114  OF    THE    BLOOD 

other  important  products  derived  from  blood,  the  removal  of 
effete  particles  and  the  substitution  of  new  ones,  and  al) 
those  changes  by  which  the  bright  blood  of  the  arteries  be 
comes  the  dark  blood  of  the  veins  ;  and  again,  in  the  cells 
of  the  respiratory  organs  which  the  capillaries  supply,  the 
dark  venous  blood  is  oxygenated  and  restored  to  the  bright 
scarlet  hue  of  the  arterial  blood. 

235.  Where  there  are  blood-vessels  in  the  lowest  animals, 

the  blood  is  kept  in  motion  by 
the  occasional  contraction  of 
some  of  the  principal  vessels, 
as  in  the  worms.  Insects  have 
a  large  vessel  running  along 
the  back,  furnished  with  valves, 
so  arranged  that,  when  the  ves- 
sel contracts,  the  blood  can 
flow  only  towards  the  head,  and,  being  thence  distributed  to 
ths  body,  is  returned  again  into  the  dorsal  vessel,  (Fig.  84,) 
by  fissures  at  its  sides. 

236.  In  all  the  higher  animals  there  is  a  central  organ, 
the  heart,  which  forces  the   blood  through  the  arteries  to- 
wards the   periphery,  and   receives  it  again  on   its  return. 
The  HEART  is  a  hollow,  muscular  organ,  of  a  conical  form, 
which  dilates  and  contracts  at  regular  intervals,  independ- 
ently of  the  will.     It  is  either  a  single  cavity,  or  is  divided 
by  walls  into  two,  three,  or  four  compartments,  as  seen  in 
the  following  diagrams.     These  modifications  are  important 
in  their  connection  with  the  respiratory  organs,  and  indicate 
the  higher  or  lower  rank  of  an  animal,  as  determined  by  the 
quality  of  the  blood  distributed  in  those  organs. 

237.  In  the  mammals  and  birds  the  heart  is  divided  by  a 
vertical  partition  into  two  cavities,  each  of  which  is  again 
divided  into  two  compartments,  one  above  the  other,  as  seen 
in  the  diagram,   Fig.  85.)    The  two  upper  cavities  are  called 


AND    CIRCULATION/  115 

auricles^  and  the  two  lower  ventricles.    Reptiles  have  two 


Fig.  85.  Fig.  86.  Fig.  87. 


auricles  and  one  ventricle,  (Fig.  86.)     Fishes  have  one  auri- 
cle and  one  ventricle  only,  (Fig.  87.) 

238.  The  auricles  do  not  communicate  with  each  other, 
in  adult  animals,  nor  do  the  ventricles.     The  former  receive 
the  blood  from  the  body  and  the  respiratory  organs,  through 
veins,  and  each  auricle  sends  it  into  the  ventricle  beneath, 
through  an  opening  guarded  by  a  valve,  to  prevent  its  reflux  ; 
while  the  ventricles,   by  their  contractions,  force  the  blood 
through  arteries  into  the  lungs,  and  through  the  body  gen- 
erally. 

239.  The  two  auricles  dilate  at  the  same  instant,  and  also 
contract  simultaneously ;  so  also  do  the  ventricles.     These 
successive  contractions  and  dilatations  constitute  the  pulsa- 
tions of  the  heart.     The  contraction  is  called  systole,  and  the 
dilatation  is  called  diastole.    Each  pulsation  consists  of  two 
movements,    the    diastole    or  dilatation    of  the    ventricles, 
during  which  the  auricles  contract,  and  the  systole  or  con- 
traction  of  the  ventricles,  while  the  auricles  dilate.     The 
frequency  of  the  pulse  varies  in  different  animals,  and  even 
in  the  same  animal,  according  to  its  age,  sex,  and  the  degree 
of  health.    In  adult  man,  they  are  commonly  about  seventy 
heats  per  minute. 

240.  The  course  of  the  blood  in  those  animals  which  have 
four  cavities  t:>  the  heart  is  as  follows,  beginning  with  the 
left  ventricle    (Fig.  85, 1.  v.)     By   the   contraction   of   this 


116  OF    THE    BLOOD 

ventricle,  the  blood  is  driven  through  the  main  arterial  trunk, 
called  the  aorta,  (Fig.  90,  a,)  and  is  distributed  by  its 
branches  thi  :>ughout  the  body  ;  it  is  then  collected  by  the 
veins,  carried  back  to  the  heart,  and  poured  into  the  right 
auricle,  (Fig.  85,  r  a,)  which  sends  it  into  the  right,  ventricle 
rv.)  The  right  ventricle  propels  it  through  another  set  of 
arteries,  the  pulmonary  arteries,  (Fig.  90,  p,)  to  the  lungs, 
(Z  ; )  it  is  there  collected  by  the  pulmonary  veins,  and  con- 
veyed to  the  left  auricle,  (Fig.  85,  /  a,)  by  which  it  is  returned 
to  the  left  ventricle,  thus  completing  the  circuit. 

241.  Hence   the   blood  in  performing   its    whole   circuit 
passes  twice  through  the  heart.     The   first  part  of  this  cir- 
cuit, the  passage  of  the   blood   through  the   body,  is  called 
the  great  circulation ;  and  the  second   part,  the  passage  of 
the  blood  through  the  lungs,  is  the  lesser  or  pulmonary  cir- 
culation :  this  double  circuit  is  said  to  be  a  complete  circu- 
lation.    In  this  case   the   heart  may  be  justly  regarded  as 
two  hearts  conjoined,  and  in  fact  the  whole  of  the  lesser  cir- 
culation intervenes  in  the  passage  of  the  blood  from  one  side 
of  the  heart  to  the  other ;  except  that  during  the  embryonic 
period  there  is  an  opening  between  the  two  auricles,  which 
closes  as  soon  as  respiration  commences. 

242.  In   reptiles,   (Fig.  86,)  the  venous  blood   from  the 
body  is  received  into  one  auricle,  and  the  oxygenated  blood 
from  the  lungs  into  the  other.     These  throw  their  contents 
into  the  single  ventricle  below,  which  propels  the  mixture  in 
part  to  the  body,  and  in  part  to  the  lungs ;  but  as  only  the 
smaller  portion  of  the  whole  quantity  is  sent  to  the  lungs  in 
a  single  circuit,  the  circulation   is  said  to  be  incomplete.     In 
the  Crocodiles,  the  ventricle  has  a  partition  which  keeps  sep 
arate  the  two  kinds  of  blood  received  from  the  auricles  ;  bui 
ihe  mixture  soon  takes  place  by  means  of  a  special  artery, 
which  passes  from  the  pulmonary  artery  to  the  aorta. 

243    In  fishes,  (Fig.   87,)  the  blood  is   carried  directly 


AND    CIRCULATION.  117 

from  the  -\  ?ntricle  to  the  gills,  which  are  their  chief  respir 
atory  organs;  thence  it  passes  into  arteries  for  distribution 
to  the  system  in  general,  and  returns  by  the  veins  to  the 
auricle.  Here  the  blood,  in  its  circuit,  passes  but  once 
through  the  heart ;  but  the  heart  of  a  fish  corresponds  nev- 
ertheless to  the  heart  of  a  mammal,  and  not  to  one  half  of 
it,  as  has  often  been  maintained,  for  the  gills  are  not  lungs. 

244.  Crabs  and  other  Crustacea  have  but  a  single  ventri- 
cle, without  an  auricle. 
In  the  mollusks,  there  is 
likewise  but  a  single  ven- 
tricle, as  in  Natica,  (Fig. 
88,  h.)  Some  have  in 
addition  one  or  two  auri- 
cles. These  auricles  are 
sometimes  so  disjoined 
as  to  form  so  many  isolated  hearts,  as  in  the  cuttle-fish. 
Among  Eadiata,  the  sea-urchins  are  provided  with  a  tubular 
heart 


CHAPTER    EIGHTH. 


OF    RESPIRATION. 


245.  F  3R  the  maintenance  of  its  vital  properties,  the  olood 
must  be  submitted  to  the  influence  of  the  air.     This  is  true 
of  all  animals,  whether  they  live  in  the  atmosphere  or  in  the 
water.     No  animal  can  survive  for  any  considerable  period 
of  time  without  air  ;  and  the  higher  animals  almost  instantly 
die  when  deprived  of  it.     It  is  the  office  of  RESPIRATION  to 
bring  the  blood  into  communication  with  the  air. 

246.  Among  animals   which   breathe    in   the   open   air, 

some  have  a  series  of  tubes  branching 
through  the  interior  of  the  body,  called 
trachea,  (Fig.  89,  *,)  opening  externally 
upon  the  sides  of  the  body,  by  small  aper- 
tures, called  stigmata,  (s  ; )  as  in  insects 
and  in  some  spiders.  But  the  most  com- 
mon mode  of  respiration  is  by  means  of 
LUNGS,  a  pair  of  peculiar  spongy  or  cel- 
lular organs,  in  the  form  of  large  pouches, 
which  are  the  more  complicated  in  pro- 
portion to  the .  quantity  of  a'r  to  be  con- 
sumed. 

247.  In  the  lower  vertebrata,  provided  with  lungs,  they 
form  a  single  organ  ;  but  in  the  higher  classes  they  are  in  pairs, 
placed  in  the  cavity  formed  by  the  ribs  one  on  each  side  of 


Fig.  89. 


OF    RESPIRATION.  119 

the  vertebral  column,  and  enclosing  the  heart  fh)  between 
them,  (Fig.  90, 1  L)  The  lungs  communicate  with  the  atmos- 
phere by  means  of  a  tube  composed  of  cartilaginous  rings 
which  arises  from  the  back  part  of  the  mouth,  and  divides 
below,  first  into  a  branch  for  each  organ,  and  then  into  in- 
numerable branches  penetrating  their 
whole  mass,  and  finally  terminating  in 
minute  sacs.  This  tube  is  the  trachea 
or  ivindpipe,  (w,)  and  its  branches  are 
the  bronchi.  In  the  higher  air-breath- 
ing animals  the  lungs  and  heart  occupy 
an  apartment  by  themselves,  the  chest, 
which  is  separated  from  the  other  con- 
tents of  the  lower  arch  of  the  vertebral 
column,  (161,)  by  a  fleshy  partition, 
called  the  diaphragm,  passing  across 
the  cavity  of  the  body,  and  arching  up  into  the  chest.  The 
only  access  to  this  apartment  from  without  is  by  the  glottis, 
(Fig.  22,  0,)  through  the  trachea. 

248.  The  mechanism  of  respiration  by  lungs  may  be  com- 
pared to  the  action  of  a  bellows.     The  cavity  of  the  chest  is 
enlarged  by  raising  the  ribs,  the*  arches  ofwhjch  naturally 
slope  somewhat  downward,  but  more  especially  by  the  con- 
traction of  the   diaphragm,  whereby  its  intrusion  into  the 
chest  is  diminished.     This  enlargment  causes  the  air  to  rush 
in  through  the  trachea,  distending  the  lung  so  as  to  nil  the 
additional  space.     When  the   diaphragm   is  again  relaxed, 
and  the  ribs  are  allowed  to  subside,  the  cavity  is  again  dimin- 
ished, and  the  air  expelled.     These  movements  are  termed 
inspiration  or  inhalation,  and  expiration.     The  spongy  pul- 
monary substance  being  thus  distended  by  air,  the  blood  sen. 
from  the  heart  is  brought  into  such  contact  with  it  as  to  allow 
the  requisite  interchange  to  take  place,  (235.) 

249.  The  respiration  of  animals  breathing  in  water  is  ac- 


120 


OF    RESPIRATION. 


Fig.  92. 

free  access  to  them 


complished   by  a   different  apparatus.     The    air   is   to   be 
/3  derived  frorr.  the  water,  in  which 

more   or  less  is  always  diffused. 
The  organs  for  this  purpose  are 
Fig.  91  called  branchiae,  or  gills,  and  are 

either  delicate  tufts  or  plumes  floating  outside  of  the  body, 
as  in  some  of  the  marine  worms, 
(Fig.  33,)  and  many  mollusks,  (Fig. 
91,  £•;)  or  they  consist  of  deli- 
cate combs  and  brushes,  as  in  fishes, 
(Fig.  92,)  crabs,  and  rnost  mollusks, 
(Fig.  88,  g.)  These  gills  are  al- 
ways so  situated  that  the  water  has 
In  the  lo^e/-  aquatic  animals,  such  as 
the  polypi,  and  some  jelly-fishes  and  mollusks,  respiration 
takes  place  by  the  incessant  motions  of  vibratory  cilia,  which 
fringe  both  the  outside  and  the  cavities  of  the  body ;  the  cur- 
rents they  produce  bringing  constantly  fresh  supplies  of  water, 
containing  air,  into  contact  with  the  respiratory  surface. 

250.  Many  animals  living  in  water,  however,  rise  to  the 
surface  and   breathe  the  atmosphere  there,  or  are  furnished 
with  the  means  of  carrying  away  a  temporary  supply  of  air, 
whilst  others  are  furnisht.d  with  reservoirs  in  which  the  blood 
requiring  oxygenation  n.ay  be  accumulated,  and  their  stay 
under  water   prolonged.     This  is  the  case  with  the  seals, 
whales,  tortoises,  frogs,  many  insects  and  mollusks,  &c. 

251.  The  vivifying  power  of  the  air  upon  the  blood  is  due 
to  its  oxygen.     If  an  animal  be  confined  for  a  time  in  a 
closed  vessel,  and  the  contained  air  be  afterwards  examined, 
a  considerable  portion  of  its  oxygen  will  have  disappeared, 
and  another  gas  <>  f  a  very  different  character,  namely,  car- 
bonic acid    gas,  will   have  taken  its   place.     The  essential 
office  of  respiration  is  to  supply  oxygen  to  the-  blood,  at  the 
same  time  fhat  carbon  is  removed  from  it. 


OF    RESPIRATION.  121 

252.  An  immediately  obvious  effect  cif  respiration  in  the 
red-blooded  animals   is  a  change    of  color;   the    blood,  in 
passing  through  the  respiratory  organs,  being  changed  from 
a  very  dark  purple  to  a  bright  scarlet.     In  the  great  circula- 
tion (241)  the  scarlet  blood  occupies  the  arteries,  and  is  usu- 
ally called  red  blood,  in  contradistinction  from  the  venous 
blood,  which  is  called  Hack  blood.     In  the  lesser  circulation, 
on  the  contrary,  the  arteries  carry  the  dark,  and  the  veins 
the  red  blood. 

253.  The  quantity  of  oxygen  consumed  by  various  am 
mals  in  a  given  time  has  been  accurately  ascertained  by  ex- 
periment.    It  has  been  found,  for  instance,  that  a  common- 
sized  man  consumes,  on  an  average,  about  150  cubic  feet  in 
twenty-four  hours ;  and  as  the  oxygen  constitutes  but  21  per 
cent,  of  the  atmosphere,  it  follows  that  he  inhales,  during  a 
day,  about  700  cubic  feet  of  atmospheric  air.     In  birds,  the 
respiration  is  still  more  active,  while  in  reptiles  and  fishes  it 
is  much  more  sluggish. 

254.  The  energy  and  activity  of  an  animal  is,  therefore 
.somewhat  dependent  on  the  activity  of  its  respiration.     Thus 
the  toad,  whose  movements  are  very  sluggish,  respires  much 
more  slowly  than  the  mammals,  birds,  and  even  insects  ;  and 
it  has  been  ascertained  that  a  butterfly,  notwithstanding  its 
comparatively  diminutive  size,  consumes  more  oxygen  than 
a  toad. 

255.  The  circulation  and  respiration  have  a  reciprocal  in- 
fluence upon  each  other.     If  the  heart  be  powerful,  or  if 
on  violent  exercise  a  more  rapid  supply  of  blood  to  repair 
the  consequent  waste  is  demanded,  (201,)  respiration  must  be 
proportionally  accelerated  to  supply  air  to  the  greater  amount 
of  blood  sent  to  the  lungs.     Hence  the  panting  occasioned  by 
running  or  other  unusual  efforts  of  the  muscles.      On  the 
other  hand,  if  respiration  be  hurried,  the  blood  is  rendered 
more  stimulating  by  greater  oxygenation,  and  ca'uses  an  ac- 

11 


122  OF    RESPIRATION. 

celeration  of  the  circulation.  The  quantity  of  air  consumed 
varies,  therefore,  with  the  proportion  of  the  blood  which  is 
sent  to  the  lungs. 

256.  The  proper  temperature  of  an  animal,  or  what  is 
termed  ANIMAL  HEAT,  depends  on  the  combined  activity  of 
the  respiratory  and  circulating  systems,  and  is  in  direct  pro- 
portion to  it.     In  many  animals  the  heat  is  maintained  at  a 
uniform  temperature,  whatever  may  be  the  variations  of  *he 
surrounding  medium.     Thus,  birds  maintain  a  temperature 
of  about  108°  Fahrenheit ;  and  in  a  large  proportion  of  mam- 
mals it  is   generally  from  95°  to   105°.     These    bear  the 
general  designation  of  warm-blooded  animals. 

257.  Reptiles,  fishes,  and  most  of  the  still  lower  animals, 
have  not  this  power  of  maintaining  a  uniform  temperature. 
The  heat  of  their  body  is  always  as  low  as  from  35°  to  50°, 
but  varies  perceptibly  with  the  surrounding  medium,  being 
often,  however,  a  little  above  it  when  the  external  tempera- 
ture is  very  low,  though  some  may  be  frozen  without  the  loss 
of  life.     For  this  reason,  they  are  denominated  cold-blooded 
animals  ;   and  all  animals  which  have  such  a  structure  of 
the  heart  that  only  a  part  of  the  blood  which  enters  it  is  sent 
to  the  respiratory  organs,  are  among  them,  (243.) 

258.  The  production  of  animal  heat  is  obviously  connected 
with  the  respiratory  process.     The  oxygen  of  the  respired 
air  is  diminished,  and  carbonic  acid  takes  its  place.     The 
carbonic  acid  is  formed  in  the  body  by  the  combination  of 
the  oxygen  of  the  air  with  the  carbon  of  the  blood.     The 
chemical    combination  attending  this  function  is,  therefore, 
essentially  the  same  as  that  of  combustion.     It  is  thus  easy 
to  understand  how  the  natural  heat  of  an  animal  is  greater 
in  proportion  a.s  respiration  is  more  active.     How  far  nutri- 
tion in  general,  and  more  particularly  assimilation,  by  which 
the  liquid  parts  are  fixed  and  solidified,  is  connected  with  the 
maintenance  of  the  proper  temperature  of  animals,  and  the 


OF    RESPMATIOIN.  123 

uniform  distribution  of  heat  through  the  body,  Its  not  yet 
been  satisfactorily  ascertained. 

259.  Some  of  the  higher  warm-blooded   animals  do  not 
maintain  their  elevated  temperature  during  the  whole  year; 
but  pass  the  winter  in  a  sort  of  lethargy  called  HIBERNATION, 
or  the  hibernating  sleep.     The  marmot,  the   bear,  the  bat, 
the  crocodile,  and  most  reptiles,  furnish  examples.     During 
this  s*ate  tfte  animal  takes  no  food  ;  and  as  it  respires  only 
after  very  prolonged  intervals,  its  heat  is  diminished,  and  its 
vital  functions  generally  are  much  reduced.     The  structural 
cause  of  hibernation  is  not  ascertained ;  but  the  phenomena 
attending  it  fully  illustrate  the  laws  already  stated,  (254-8.) 

260.  There  is  another  point  of  view  in  which  respiration 
should  be  considered,  namely,  with  reference  to  the  buoy- 
ancy of  animals,  or  their  power  of  rising  in  the  atmosphere, 
and  their  ability  to  live  at  different  depths  in  the  water,  under 
a   diminished    or   increased  pressure.     The  organs  of  res- 
piration of  birds  and  insects  are  remarkably  adapted  for  the 
purpose  of  admitting  at  will  a  greater  quantity  of  air  into 
their  body,  the  birds  being  provided  with  large  pouches  ex- 
tending from  the  lungs  into  the   abdominal  cavity  and  into 
the  bones  of  the  wing.      In   insects  the  whole  be  dy  is  pene- 
trated by  air  tubes,  the  ramifications  of  their  tracheae,  which 
are  enlarged  at  intervals  into  wider  cells  ;  whilst  most  of  the 
aquatic   animals    are  provided  with  minute,  almost   micro- 
scopic tubes,  penetrating  from  the  surface  into  the  substance, 
or  the  cavities  of  the  body,  admitting  water  into  the  interior, 
by  which  they  thus  adapt  their  whole  system  to  pressures 
which  would  otherwise  crush  them.     These  tubes  may  with 
propriety  be  called  water-tubes.     In   fishes,  they  penetrate 
through  the  bones  of  the   head   and  shoulder,  through  skin 
and   scales,  and   communicate  with   the   blood   vessels   and 
heart,  into  which   they   pour  water ;  in  mollusks  they  are 
more  mnrerous  in  the  fleshy  parts,  as,  for  example,  in  the 


124  OF    RESPIRATION. 

foot,  which  they  help  to  distend,  and  communicate  with  the 
main  cavity  of  the  body,  supplying  it  also  with  liquid  ^  in 
echinoderms  they  pass  through  the  skin,  and  even  through 


260  a.  In  order  fully  ;o  appreciate  the  homologies  between  the 
various  respiratory  apparatus  observed  in  different  animals,  it  is  ne- 
cessary to  resort  to  a  strict  comparison  of  the  fundamental  connec- 
tions of  these  organs  with  the  whole  system  of  organization,  rather 
than  to  the  consideration  of  their  special  adaptation  to  the  elements 
in  which  they  live.  In  Vertebrates,  for  instance,  there  are  two  seta 
of  distinct  respiratory  organs,  more  or  less  developed  at  different  pe- 
riods of  life,  or  in  different  groups.  All  Vertebrates,  at  first,  have 
gills  arising  from  the  sides  of  the  head,  and  directly  supplied  with 
blood  from  the  heart ;  but  these  gills  are  the  essential  organs  of  res- 
piration only  in  fishes  and  some  reptiles,  and  gradually  disappear 
in  the  higher  reptiles,  as  well  as  in  birds  and  Mammalia,  towards 
the  close  of  their  embryonic  growth.  Again,  all  Vertebrates  have 
lungs,  opening  in  or  near  the  head ;  but  the  lungs  are  fully  devel- 
oped only  in  Mammalia,  birds,  and  the  higher  reptiles,  in  propor- 
tion as  the  branchial  respiration  is  reduced ;  whilst  in  fishes  the  air- 
bladder  constitutes  a  rudimentary  lung. 

260  b.  In  Articulates,  there  are  also  two  sorts  of  respiratory  or- 
gans ;  aerial,  called  tracheae  in  insects,  and  lungs  in  spiders  ;  and 
aquatic,  in  Crustacea  and  worms,  called  gills.  But  these  tracheae  and 
lungs  open  separately  upon  the  two  sides  of  the  body,  (air  never 
being  admitted  through  the  mouth  or  nostrils  in  Articulates ;)  the 
gills  are  placed  in  pairs  ;  those  which  are  like  the  tracheae  occupying 
a  similar  position,  so  that  there  are  nearly  as  many  pairs  of  tracheae 
and  gills  as  there  are  segments  in  these  animals,  (Figs.  89  and  33.) 
The  different  respiratory  organs  in  Articulates  are  in  reality  mere 
modifications  of  the  same  apparatus,  as  their  mode  of  formation  and 
successive  metamorphoses  distinctly  show,  and  cannot  be  compared 
•with  either  the  lungs  or  gills  of  Vertebrates  ;  they  are  special  organs 
not  found  in  other  classes,  though  they  perfi  rm  the  same  functions. 
The  same  may  be  said  of  the  gills  and  lungs  of  mollusks,  which 
are  essentially  alike  in  structure,  the  lungs  of  snails  and  slugs  being 
only  a  modification  of  the  gills  of  aquatic  mollusks  ;  but  these  two 
kinds  of  organs  differ  again  in  their  structure  and  relations  from  the 
tracheae  and  gills  of  Articulates,  as  much  as  from  the  lungs  and  gills 


OF    RESPIRATION.  125 

i.he  hard  shell,  whilst  in  polyps  they  perforate  the  walls  of 
the  ge.ieral  cavity  of  the  body,  which  they  constantly  fili 
with  water. 


of  Vertebrates.  In  those  Radiates  which  are  provided  with  distinct 
respiratory  organs,  such  as  the  Echinoderms,  we  find  still  anothei 
typical  structure,  their  gills  forming  bunches  of  fringes  around  the 
mouth,  or  rows  of  minute  vesicles  along  the  radiating  segments  of 
ttib  body. 

11* 


CHAPTER    NINTH. 

OF    THE    SECRETIONS. 

261.  V/u  LE,  by  the  process  of  digestion,  a  homogeneous 
fluid  is  prepared  from  the  food,  and  supplies  new  material  to 
»he  blood,  another  process  is  also  going  on,  by  which  the 
blood  is  analyzed,  as  it  were  ;  some  of  its  constituents  being 
selected   and  so   combined   as  to  form   products  for  useful 
purposes,  while  other  portions  of  it  which  have  become  useless 
or  injurious  to  the  system  are  taken  up  by  different  organs, 
and    expelled   in  different   forms.     This  process  is  termed. 
SECRETION. 

262.  The  organs   by  which    these    operations   are    per- 
formed are  much  varied,  consisting  either  of  flat  surfaces  or 
membranes,  of  minute  simple  sacs,  or  of  delicate  elongated 
tubes,  all  lined   with  minute  cells,  called  epithelium  cells, 
which  latter  are  the  real  agents  in  the  process.     Every  sur- 
face of  the  body  is  covered  by  them,  and  they  either  dis- 
charge their  products  directly  upon  the  surface,  as  on  the 
mucous  membrane,  or  they  unite  in  clusters  and  empty  into 
a  common  duct,  and  discharge  by  a  single  orifice,  as  is  the 
case  with  some  of  the  intestinal  glands,  and  of  those  from 
which  the  perspiration  issues  upon  the  skin,  (Fig.  94.) 


OF    THE    SECRETIONS  127 

263.  In   the    .:igher    animals,   where 
separate  organs  for  special  purposes  are 
multiplied,  numerous  sacs  and  tubes  are 
assembled    into    compact  masses,  called 
glands.     Some  of  these  are  of  large  size, 
such  as  the  salivary  glands,  the   kidneys, 
and  Vie  liver.     In  these,  clusters  of  sacs 
open  into  a  common  canal,  and  this  canal 

unites  with  similar  ones  forming  larger  trunks,  such  as  we 
find  in  the  salivary  glands,  (Fig.  93,)  and  finally  they  all 
discharge  by  a  single  duct. 

264.  By  the  organs  of  secretion,  two  somewhat  different 
purposes  are  effected,  namely,  fluids  of  a  peculiar  character 
are  selected  from  the  blood,  for  important  uses,  such  as  the 
saliva,  tears,  milk,  &c.,  some  of  which    differ  but  little  in 
their  composition  from  that  of  the  blood  itself,  and   might 
be   retained    in   the    blood    with    impunity ;     or,    the    fluids 
selected   are  such   as   are    positively  injurious,  and  cannot 
r3main   in  the  blood   without  soon   destroying  life.     These 

atter  are  usually  termed  EXCRETIONS. 

.  265.  As  the  weight  of  the  body,  except  during  its  period 
of  active  growth,  remains  nearly  uniform,  it  follows  that  it 
must  daily  lose  as  much  as  it  receives ;  in  other  words,  the 
excretions  must  equal  in  amount  the  food  and  drink  taken, 
with  the  exception  of  the  small  proportion  discharged  by  the 
alimentary  canal.  Some  of  the  most  important  of  these 
outlets  will  be  now  indicated. 

266.  We  have  already  seen  (37)  that  all  animal  tissues 
admit  of  being  traversed  by  liquids  and  gases.  This  mutual 
transmission  of  fluids  from  one  side  of  a  membrane  to  the 
other  is  termed  endosmosis  and  exosmosis,  or  imbibition  and 
transudation,  and  is  a  mechanical,  rather  than  a  vital,  phe- 
nomenon, inasmuch  as  it  takes  place  in  dead  as  well  as  in 


128  OF    THE    SECRETIONS. 

living  tissues.  The  bloodvessels,  especially  the  capillaries, 
share  this  property.  Hence  portions  of  the  circulating  fluids 
escape  through  the  walls  of  the  vessels  and  pass  off  at  the 
surface.  This  superficial  loss  is  termed  exhalation.  It  is 
most  active  where  the  bloodvessels  most  abound,  and  accord 
ingly  is  very  copious  from  the  air-tubes  of  the  lungs  and 
from  the  skin.  The  loss  in  this  way  is  very  considerable  ; 
and  it  has  been  estimated  that,  under  certain  circumstances, 
the  body  loses,  by  exhalation,  five  eighths  of  the  whole  weight 
of  the  substances  received  into  it. 

267.  The  skin,  or  outer  envelop  of  the  body,  is  otherwise 
largely  concerned    in    the   losses   of  the  body.     Its  layers 
are    constantly   renewed    by  the    tissues  beneath,  and    the 
outer  dead  layers  are  thrown  off.     This  removal  is  some- 
times gradual  and  continual,  as  in  man.     In  fishes  and  many 
mollusks,  it  comes  off  in  the  form  of  slime,  which  is,  in  fact, 
composed  of  cells  detached  from    the  surface  of  the  skin. 
Sometimes  the  loss  is  periodical,  when  it  is  termed  moulting. 
Thus,  the  mammals  cast  their  hair,  and  the  deer  their  horns, 
the  birds  their  feathers,  the  serpents  their  skins,  the  crabs 
their  test,  the  caterpillars  their  outer  envelop,  with  all  the 
hairs  growing  from  it. 

268.  The  skin  presents  such  a  variety  of  structure  in  the 
different  groups  of  animals  as  to  furnish  excellent  distinctive 
characters  of  species,  genera,  and    even  families,  as  will 
hereafter  be  shown.     In  the  vertebrates  we  may  recognize 
several  distinct  layers,  of  unequal  thickness,  as  may  be  seen 
in  figure  94,  which  represents  a  magnified  section  of  the 
human   skin,  traversed    by  the    sudoriferous   canals.     The 
lower  and  thickest  layer,  (a,)  is  the  cutis,  or  true  skin,  and 
is  the  part  which  is  tanned  into  leatner.     Its  surface  presents 
numerous  papillae,  in  which  the  nerves  of  general  sensation 
terminate;  they  also  contain  a  fine  network  of  bloodvessels, 


OF    THE  SECRETIONS. 


129 


Fig.  94. 


usually  termed  the  vascular  layer.  The 
Bupsrficial  layer  (c)  is  the  epidermis, 
or  cuticle.  The  cells  of  which  it  is  com- 
posed are  distinct  at  its  inner  portion, 
but  become  dried  and  flattened  as  they 
are  pushed  outwards.  It  is  supplied  with 
neither  vessels  nor  nerves,  and,  conse- 
quently, is  insensible.  Between  these 
two  layers,  and  more  especially  con- 
nected with  the  cuticle,  is  the  rele  muco- 
sum,  (1),)  a  very  thin  layer  of  cells,  some 
of  which  contain  the  pigment  which 
gives  the  complexion  to  the  different 
races  of  men  and  animals.  The  scales 
of  reptiles,  the  nails  and  claws  of 
mammals,  and  the  solid  coverings  of  the  Crustacea,  are 
merely  modifications  of  the  epidermis.  On  the  other  hand, 
the  feathers  of  birds  and  the  scales  of  fishes  arise  from  the 
vascular  layer. 

269.  Of  all  the  Excretions,  if  we  except  that  from  the 
Lungs,  the  bile  seems  to  be  the  most  extensive  and  im- 
portant ;  and  hence  a  liver,  or  some  analogous  organ,  by 
which  bile  is  secreted,  is  found  in  animals  of  every  depart- 
ment ;  while  some,  or  all,  of  the  other  glands  are  want- 
ing in  the  lower  classes  of  animals.  In  Vertebrates,  the 
liver  is  the  largest  of  all  the  organs  of  the  body.  In  rnol- 
lusks,  it  is  no  less  preponderant.  In  the  gasteropods,  like  the 
snail,  it  envelopes  the  intestine  in  its  convolutions,  (Fig.  52  ;) 
and  in  the  acephala,  like  the  clam  and  oyster,  it  generally 
surrounds  the  stomach.  In  insects  it  is  found  in  the  shape  of 
long  tubes,  variously  contorted  and  interlaced,  (Fig.  51.)  In 
the  Radiata,  this  organ  is  largely  developed,  especially 
among  the  echinoderms.  In  the  star-fishes  't  extenis  into 


130  OF    THE    SECRETIONS. 

all  the  recesses  cf  the  rays  ;  and,  in  color  and  stiuctuie,  re 
sembles  the  liver  of  mollusks.  Even  in  polyps,  we  find  pe- 
culiar brDwn  cells  lining  the  digestive  cavity,  which,  proba- 
bly, perform  functions  similar  to  those  of  the  liver  in  the 
higher  animals. 

270.  The  great  importance  of  the  respiratory  organs  in 
discharging  carbon  from  the  blood  has  already  been  spoken 
of,  (245,  251.)  The  substances  removed  by  the  liver  and 
the  lungs  are  of  the  same  class,  being  those  which  are  desti- 
tute of  nitrogen.  These  organs  seem,  in  some  sense,  sub- 
sidiary to  each  other ;  and  hence,  in  those  animals  where 
the  respiratory  organs  are  largely  developed,  the  biliary 
organs  are  comparatively  small,  and  vice  versa.  Another 
and  opposite  class  of  impurities,  and  no  less  pernicious  if 
retained  in  the  blood,  is  removed  by  the  KIDNEYS  ;  and, 
consequently,  organs  answering  to  the  kidneys  are  found 
very  far  down  in  the  series  of  animals.  Most  of  the  peculiar 
ingredients  of  the  urine  are  capable  of  assuming  solid,  crys- 
talline forms ;  and,  in  some  animals,  as  in  reptiles  and 
birds,  the  whole  secretion  of  the  kidneys  is  solid.  In  mosi 
cases,  however,  the  urinary  salts  are  largely  diluted  with 
water;  and,  as  the  lungs  and  liver  are  supplementary  to 
each  other  in  the  removal  of  carbon,  so  the  lungs,  the  kid- 
neys, and  the  skin  mutually  relieve  each  other  in  the  removal 
of  the  watery  portions  of  the  blood. 


CHAPTER    TENTH 

EMBRYOLOGY. 
SECTION    I 

OF    THE    EGG. 

271.  THE  functions  of  vegetative  life,  of  which  we  nave 
treated  in  the  preceding  chapters,   namely,  digestion,  circu- 
lation, respiration,  and  secretion,  have  for  their  end  the  pres- 
ervation of  the   individual.     We  have  now  to  treat  of  the 
functions   that  serve  for   the    perpetuation   of  the   species, 
namely   those  of  reproduction,  (200.) 

272.  It  has  been  generally  admitted  that  animals  as  well 
as  plants  are  the  offspring  of  individuals  of  the  same  kind  ; 
and  vice  versa,  that  none  of  them  can   give  birth  to  individ- 
uals  differing   from  themselves ;  but   recent   investigations 
have  modified  to  a  considerable  extent  this  view,  as  we  shall 
see  hereafter. 

273.  Reproduction  in  animals  is  almost  universally  accom 
plished  by  the  association  of  individuals  of  two  kinds,  males 
and  females,  living  commonly  in  pairs  or  in  flocks,  each  of 
them  characterized  by  peculiarities  of  structure  and  external 
appearance.     As  this  distinction  prevails  throughout  the  ani- 
mal kingdom,  it  is  always  necessary,  if  we   would  obtain  a 
correct  and  complete  idea  of  a  species,  to  take  into  account 
the  peculiarities  of  both  sexes.     E  veiy  one  is  familiar  with  the 
differences  between  the  cock  and   the  hen,  the  lion  and  the 
lioness,  frc.     Less  prominent  peculiarities  are  observed  in 


132  EMBRYOLOGY. 

most  Vertebrates.  Among  Articulata,  the  differences  are  no 
less  striking,  the  males  being  often  of  a  different  shape  and 
color,  as  in  crabs,  or  having  even  more  complete  organs,  as 
in  many  Bribes  of  insects,  where  the  males  have  wings,  while 
the  females  are  destitute  of  them,  (Fig.  1-17.)  Among  mol- 
lusks,  the  females  have  often  a  wider  shell. 

2,74.  Even  higher  distinctions  than  specific  ones  are  based 
upon  peculiarities  of  the  sexes ;  for  example,  the  whole 
class  of  Mammalia  is  characterized  by  the  fact  that  the 
female  is  furnished  with  organs  for  nourishing  her  young 
with  a  peculiar  liquid,  the  milk, secreted  by  herself.  Again, 
the  Marsupial,  such  as  the  opossum  and  kangaroo,  are  dis- 
tinguished by  the  circumstance  that  the  female  has  a  pouch 
into  which  the  young  are  received  in  their  immature  con- 
dition at  birth. 

275.  That  all   animals  are  produced  from  eggs,  (Omne 
vivum  ex  ovo,)  is  an  old  adage  in  Zoology,  which  modern 
researches  have  fully  confirmed.     In  tracing  back  the  phases 
of  animal  life,  we  invariably  arrive  at  an  epoch  when  the 
incipient  animal  is  enclosed  within  an  egg.     It  is  then  called 
an  embryo,  and   the  period  passed  in  this  condition  is  called 
the  embryonic  period. 

276.  Before  the   various  classes  of  the  animal  kingdom 
had  been  attentively  studied  during  the  embryonic  period, 
all  animals  were  divided  into  two  great  divisions  :  the  ovip- 
arous,   comprising    those    which    lay   eggs,  such    as    birds, 
reptiles,  fishes,  insects,  mollusks,  &c.,  and  the  viviparous, 
which  bring  forth  their  young  alive,  like  the  mammalia,  and 
a  few  from  other  orders,  as  the  sharks,  vipers,  &c.     This 
distinction  lost  much  of  its  importance  when  it  was  shown 
that  viviparous  animals  are  produced  from  eggs,  as  well  as 
the   oviparous ;  only  that  their  eggs,  instead   of   being  laid 
before  the  development  of  the  embryo  begins,  undergo  their 
early  changes  in  the  body  of  the  mother.     Production  from 


OF    THE    EGG. 


133 


Fig.  95. 


egga  should   therefore,  be  considered  as  a  universal  charac 
terislic  of  the  Animal  Kingdom. 

277.  Form  of  the   Egg.  —  The  general  form  of  the  egg 
is  more  or  less  spherical.     The  eggs  of  birds  have  the  form 
of  an    elongated    spheroid,  narrow    at   one   end ;    and    this 
form  is  so  constant,  that  the  term  oval  has  been  universally 
adopted  to  designate  it.     But  this  is  by  no  means  the  usua' 
form  of  the  eggs  of  other  animals. 

Fn  most  instances,  on  the  contra- 
ry they  are  spherical,  especially 
among  the  lower  animals.  Some 
have  singular  appendages,  as  those 
of  the  skates  and  sharks,  (Fig.  95,)  which  are  shaped  like 
a  hand-barrow,  with  four  hooked  horns  at  the  corners.  The 
eggs  of  the  hydra,  or  fresh  water 
polyp,  are  thickly  covered  with 
prickles,  (Fig.  96.)  Those  of 
certain  insects",  the  Podurella,  for 
example,  are  furnished  with  fila- 
ments which  give  them  a  hairy 
aspect,  (Fig.  97 ;)  others  are  cylindrical  or  prismatic ;  and 
frequently  the  surface  is  sculptured. 

278.  Formation' of  the  Egg.  —  The  egg  originates  within 
peculiar  organs,  called  ovaries,  which  are  glandular  bodies, 
usually  situated  in  the  abdominal  cavity.     So  long  as  the 
eggs  remain  in  the  ovary,  they  are  very  minute  in  size,     in 
this  condition  they  are  called  ovarian,  or  primitive  eggs. 
They  are   identical   in  all  animals,  being,  in 

fao.t,  merely  little  cells  (v)  containing  yolk, 
(yy)  and  including  other  smaller  cells,  the 
germinative  vesicle,  (g,)  and  the  germinative 
dotf,  (d.)  The  yolk  itself,  with  its  membrane, 
(v,)  is  formed  while  the  egg  remains  in  the 
ovary.  It  is  afterwards  enclosed  in  another 
envelope,  the  shell  membrane,  which  may  remain  soft, 
12 


Fig.  96. 


Fig.  97- 


Fig.  98. 


134  EI I  BRYOLOGY. 

or  be  further  surrounded  by  calcareous  deposits,  the  shell 
proper,  (Fig.  101,  5.)  The  number  of  these  eggs  is  large,  in 
proportion  as  the  animal  stands  lower  in  the  class  to  which 
it  belongs.  The  ovary  of  a  herring  contains  more  than 
25,000  eggs;  while  that  of  birds  contains  a  much  smaller 
number  perhaps  one  or  two  hundred  only. 

279.  Ovulation.  —  Having  attained  a  certain  degree  of 
maturity,  which  varies  in   different  classes,  the  eggs  leave 
the  ovary.     This  is  called  ovulation,  and  must  not  le  con- 
founded with  the  laying  of  the  eggs,  which  is  the  subsequent 
expulsion  of  them  from  the  abdominal  cavity,  either  imme- 
diately, or  through  a  special  canal,  the  oviduct.     Ovulation 
takes  place  at  certain  seasons  of  the  year,  and  never  be- 
fore   the   animal    has  reached    a   particular  age,  which    is 
commonly  that  of  its  full  growth.     In  a  majority  of  species} 
ovulation  is  repeated  for  a  number  of  years  consecutively, 
generally  in  the  spring  in  terrestrial  animals,  and  frequently 
several  times  a  year ;  most  of  the  lower  aquatic  animals,  how- 
ever* lay  their  eggs  in  the  fall,  or  during  winter.     In  others, 
on  the  contrary,  it  occurs  but  once  during  life,  at  the  period  of 
maturity,  and  the  animal  soon  afterwards  dies.     Thus  the  but- 
terfly and  most  insects  die,  shortly  after  having  laid  their  eggs. 

280.  The  period  of  ovulation  is  one  of  no  less  interest  tc 
the   zoologist  than  to  the   physiologist,  since    the    peculiai 
characteristics  of  each  species  are  then  most  clearly  marked. 
Ovulation  is  to  animals  whit  flowering  is  to  plants  ;   and, 
indeed,  few  phenomena  are  more  interesting  to  the  student 
of  nature  than  those  exhibited  by  animals  at  the  pairing 
season.      Then   their   physiognomy  is   the  most  animated, 
their  song  the   most  melodious,  and  their   attire  the    most 
brilliant.     Some  birds  appear  so  different  at  this  time,  that 
zoologists  are  always  careful  to  indicate  whether  or  not  a 
bird   is  represented  at  the   breeding  season.      Fishes,  and 
many  other  animals,  are   ornamented   with  much  brighter 
colo-s  at  this  period 


OF    THE    EGG. 


135 


281.  Laying.  —  After  leaving  the  ovary,  the   eggs   are 
either  discharged   from  the   animal,  that   is,  laid  ;  or  they 
continue  their  development  within  the  parent  animal,  as  is 
the  case  in  some  fishes  and  reptiles,  as  sharks  and  vipers, 
which,  for    that  reason,  have  been   named    ovo-viviparous 
animals.     The  eggs  of  the  mammalia  are  not  only  developed 
within  the  mother,  but  become  intimately  united  to  her  ;  this 
peculiar  mode  of  development  has  received  the  name  of 
gestation. 

282.  Eggs  are  sometimes  laid  one  by  one,  as  in  birds ; 
sometimes  collectively  and  in  great  numbers,  as  in 

the  frogs,  the  fishes,  and  most  of  the  invertebrates. 
The  queen  ant  of  the  African  termites  lays  80,000 
eggs  in  twenty-four  hours  ;  and  the  common  hair- 
worm, (Gordius,)  as  many  as  8,000,000  in  less  than 
one  day.      In  some  instances  they  are    united  in 
clusters  by  a  gelatinous  envelop  ;  in  others  they  are    Fi 
enclosed    in   cases  or    between  membranous  disks, 
forming  long  strings,  as  in  the  eggs  of  the  Pyrula  shell,  (Fig 
99.)      The  conditions  under  which  the  eggs 
of  different  animals  are  placed,  on  being  laid, 
are  very  different.     The  eggs  of  birds,  and  of 
some  insects,  are  deposited  in  nests  constructed 
for  thc»t  purpose  by  the  parent.     Other  animals 
carry  their   eggs    attached    to    their  bodies  ; 
sometimes  under  the  tail,  as  in  the    lobsters 
and  r  rabs,  sometimes  hanging  in  large  bun- 
dles nn   both  sides  of  the  tail,  as  in  the  Mo- 
nocul-is,  (Fig.  100,  a.) 

233.  Some  toads  carry  them  on  the  back,  and,  what  is 
most  extraordinary,  it  is  the  male  which  undertakes  this 
olfice.  Many  mollusks,  the  Unio  for  example,  have  them 
enclosed  between  the  folds  of  the  gills  during  incubation, 
In  the  jelly  fishes  and  polyps,  they  hang  in  clusters,  either 


Fig.  100. 


136  EMBRYOLOGY. 

outside,  (Fig.  77,  o,)  or  inside,  at  the  bottom  of  tie  cavity 
of  the  body.  Some  insects,  such  as  the  gad-flies,  deposit 
their  eggs  on  other  animals.  Finally,  many  abandon  their 
eggs  to  the  elements,  taking  no  further  care  of  them  after 
they  have  been  laid  ;  such  is  the  case  with  most  fishes,  some 
insects,  and  many  mollusks.  As  a  general  rule,  it  may  be 
said  that  animals  take  the  more  care  of  their  eggs  and  brood 
as  they  occupy  a  higher  rank  in  their  respective  classes. 

284.  The  development   of  the  embryo  does  not  always 
take  place  immediately  after  the  egg  is  laid.     A  considera- 
ble time,  even,  may  elapse  before  it  commences.     Thus,  the 
first  eggs  laid  by  the  hen  do  not  begin  to  develop  until  the 
whole  number  which  is  to  constitute  the  brood  is  deposited. 
The  eggs  of  most  butterflies,  and  of  insects  in  genelal,  are 
laid  in  autumn,  in  temperate  climates,  and  remain  unchanged 
until  the  following  spring.     During  this  time,  the  principle 
of  life  in  the  egg  is  not  extinct,  but  is  simply  inactive,  or  in 
a  latent  state.     This  tenacity  of  life  is  displayed  in  a  still 
more   striking   manner   in    plants.     The   seeds,  which  are 
equivalent  to  eggs,  preserve  for  years,  and  even  for  ages 
their    power   to  germinate.      Thus,  there   are    some   well- 
authenticated  cases  in  which 'wheat  taken  from  the  ancient 
catacombs  of  Egypt  has  been  made  to  sprout  and  grow. 

285.  A   certain    degree    of  warmth  is  requisite   for  the 
hatching  of  eggs.     Those  of  birds,  especially,  require  to  be 
submitted,  for  a  certain   length  of  time,  to  a  uniform  tem- 
perature, corresponding  to  the  natural  heat  of  the   future 
chicken,  which  is  naturally  supplied    by  the   body  of  the 
parent.     In  other  words,  incubation  is  necessary  for  t«heir 
growth.     Incubation,  however,  is  not  a  purely  vital  phenom- 
enon, but  may  be   easily  imitated  artificially.     Some  birds 
of  warm  climates  dispense  with  this  task  ;  for  example,  the 
ostrich  often  contents  herself  with  depositing  her  eggs  in  the 
sand  of  the  desert,  lea  ing  them  to  be  hatched  by  the  gun.     In 


OF    THE    EGG.  137 

like  manner,  th?  eggs  of  most  birds  may  be  hatched  by  main- 
taining them  at  the  proper  temperature  by  artificial  means. 
Some  fishes  are  also  known  to  build  nests  and  to  sit  upon 
their  »;ggs,  as  the  sticklebacks,  sun-fishes,  and  cat-fishes  ;  but 
whether  they  impart  heat  to  them  or  not,  is  doubtful. 

Before  entering  into  the  details  of  embryonic  transfer 
mations,  a  few  words  are  necessary  respecting  the  composi 
tion  of  the  egg. 

286.  Composition  of  the  Egg.  —  The  egg  is  composed 
of  several  substances,  varying  in  structure,  as  well  as  in 
appearance.     Thus,  in  a  hen's  egg,  (Fig.  101,)  we  have  first 
a  calcareous  shell,  (s,)  lined  by  a  double  membrane,  the  shell 
membrane,  (m ;)  then  an  albuminous  substance,    the  white, 
(a,)  in  which  several  layers  may  be  distinguished ;    within 
this  we  find  the  yolk,  (y,)  enclosed  in  its  membrane ;  and 
before  it  was  laid,  there  was  in  the  midst  of  the  latter  a  mi- 
nute vesicle,  the  germinative  vesicle,  (Fig.  98,  g,)  containing 
a  still  smaller  one,  the  germinative  dot*  (d.)     These  different 
parts  are  not  equally  important  in  a 

physiological  point  of  view.  The 
most  conspicuous  of  them,  namely, 
the  shell  and  the  white,  are  not  es- 
sential parts,  and  therefore  are  often 
wanting ;  while  the  yolk,  the  ger- 
minative vesicle,  and  the  germina-  Fig.  101 
tive  dot  are  found  in  the  eggs  of 

all  animals  ;  and  out  of  these,  and  of  these  only,  the  germ  is 
formed,  in  the  position  shown  by  Fig.  101,  e. 

287.  The  vitellus  or  yolk  (Fig.  101,  y)  is  the  most  essen- 
tial part  of  the  egg.     It  is  a  liquid  of  variable  consistence, 
sometimes  opaque,  as  in  the  eggs  of  birds,  sometimes  trans- 
parent and  colorless,   as  in  the  eggs    of  some   fishes  and 
mollusks.     On  examination  under  the  microscope,  it  appears 
to  be  composed  of  an  accumulation  of  granules  and  oil-drops. 

12* 


138  EMBRYOLOGY. 

The  yelk  is  surrounded  by  a  very  thin  skin,  the  vitellme 
membrane,  'Fig.  98,  v.)  In  some  insects,  when  the  albumen 
is  wanting,  this  membrane,  surrounded  by  a  layer  of  pecu- 
liar cells,  forms  the  exterior  covering  of  the  egg,  which,  in 
sucli  cases,  is  generally  of  a  firm  consistence,  and  sometimes 
even  horny. 

288.  The  germinative  vesicle  (Fig.  98,  g)  is  a  cell  of  ex- 
treme delicacy,  situated,  in  the  young  egg,  near  the  middle 
of  the  yolk,  and  easily  recognized  by  the  greater  transpar- 
ency of  its  contents  when  the  yolk  is  in  some  degree  opaque, 
as  in  the  hen's  egg,  or  by  its  outline,  when  the  yolk  itself  is 
transparent,  as  in  eggs  of  fishes  and  mollusks.     It  contains 
one  or  more  little  spots,  somewhat  opaque,  appearing   as 
small  dots,  the  germinal  dots,  (rf.)     On  closer  examination, 
these  dots  are  themselves  found  to  contain  smaller  nucleoli. 

289.  The  albumen,  or  white  of  the  egg,  (Fig.  101,  a,)  is 
a    viscous    substance,    generally   colorless,    but    becoming 
opaque  white  on  coagulation.     Voluminous  as  it  is  in  birds' 
eggs,  it  nevertheless  plays  but  a  secondary  part  in  the  histo- 
ry of  their  development.     It  is  not  formed  in  the  ovary,  like 
the  yolk,  but  is  secreted  by  the  oviduct,  and  deposited  around 
the  yolk,  during  the  passage  of  the  egg  through  that  canal. 
On  this  account,  the  eggs  of  those  animals  in  which  the  ovi 
duct  is  wanting,  are  generally    without  the  albumen.      In 
birds,  the  albumen  consists  of  several  layers,  one  of  which, 
the  chalaza,  (c,)  is  twisted.     Like  the  yolk,  the  albumen  is 
surrounded  by  a  membrane,  the  shell  membrane,  (m,)  which 
is  either  single    or   double,  and  in  birds,  as  also  in  some 
reptiles  and   mollusks,  is   again  protected  by   a  calcareous 
covering,  forming  a  true  shell,  (s.)     In  most  cases,  how- 
ever, tbis  envelop  continues  membranous,  particularly  in  the 
eggs  of  the  mollusks,  most  crustaceans  and  fishes,  salaman- 
ders, frogs,  &c.     Sometimes  it  is  horny,  as  in  the  sharks 
and  skates. 


DEVELOPMENT  OF  THE  YOUNG  WITHIN  THE  ECG.   139 


SECTION  H. 

DEVELOPMENT  OF  THE  YOUNG  WITHIN  THE  EGG. 

290.  The  formation  and   development  of  the  young  ani- 
mal within  the  egg  is  a  most  mysterious  phenomenon.  From 
a  hen's  egg,  for  example,  surrounded  by  a  shell,  and  com- 
posed, as  we  have   seen,  (Fig.  101,)   of  albumen  and  yolk, 
with  a  minute  vesicle  in  its  interior,  there  is  produced,  at  the 
end  of  a  certain  time,  a  living  animal,  composed  apparently 
of  elements  entirely  different   from  those  of  the  egg,  en- 
dowed with  organs  perfectly  adapted  to  the  exercise  of  all 
the  functions  of  animal  and  vegetative   life,  having  a  pul- 
sating heart,  a  digestive  apparatus,  organs  of  sense  for  the 
reception  of  outward  impressions,  and  having,  moreover,  the 
faculty    of  performing  voluntary   motions,   and   of  experi- 
encing pain  and  pleasure.     These  phenomena  are  certainly 
sufficient  to  excite  the  curiosity  of  every  intelligent  person. 

291.  By  opening  eggs  which  have  been  subjected  to  incu- 
bation during  different  periods  of  time,  we  may  easily  satisfy 
ourselves  that  these  changes  are   effected  gradually.     We 
thus  find  that  those  which  have  undergone  but  a  short  incu- 
bation exhibit  only  faint  indications  of  the  future  animal ; 
while    those   upon  which   the    hen   has   been  sitting  for  a 
longer    period   include    an   embryo  chicken    proportionally 
more  developed.     Modern  researches  have  taught  us  that 
these  gradual  changes,  although  complicated,  and  at  first 
sight  so   mysterious,  follow  a   constant  law  in  each  great 
division  of  the  Animal  Kingdom.  * 

292.  The  study  of  these  changes  constitutes  that  peculiar 
branch  of  Physiology  called   EMBRYOLOGY.     As  there  are 
differences   in  the  four  great  departments   of  the   AnimaJ 


140  EMBRYOLOGY. 

Kingdom  perceptible  at  an  early  stage  of  embryonic  life, 
quite  as  obvious  as  those  found  at  maturity,  and  as  the 
phases  of  embryonic  development  furnish  important  indi- 
cations for  the  natural  classification  of  animals,  we  propose 
to  give  the  outlines  of  Embryology,  so  far  as  it  may  have 
reference  to  Zoology. 

293.  In  order  to  understand  the   successive  steps  of  em- 
bryonic development,  we  must  bear  in  mind  that  the  whole 
animal  body  is  formed  of  tissues,  the  elements  of  which  are 
cells,  (39.)     These  cells,  however,  are  more  or  less  diversi- 
fied and  modified,  or  even  completely  metamorphosed  in  the 
full  grown  animal ;  but,  at  the  commencement  of  embry- 
onic life,  the  whole  embryo  is  composed  of  minute  cells  of 
nearly  the  same  form  and  consistence,  originating  within  the 
yolk,  and  constantly  undergoing  changes  under  the  influence 
of  life.     New  cells  are   successively  formed,  while  others 
disappear,  or  are  modified  and  so  transformed  as  to  become 
bones,  muscles,  nerves,  &c. 

294.  We  may  form  some  idea  of  this  singular  process, 
by  noticing  how,  in  the  healing  of  a  wound,  new  substance 
is  supplied  by  the  transformation  of  blood.     Similar  changes 
take  place  in  the  embryo,  during  its  early  life  ;  only,  instead 
of  being  limited  to  some  part  of  the  body,  they  pervade  the 
whole  animal. 

295.  The  changes  commence,  in  most  animals,  soon  after 
the  eggs  are  laid,  and  are  continued  without  interruption 
until  the  development  of  the  young  is  completed ;  in  others, 
birds  for  example,  they  proceed  only  to  a  certain  extent,  and 
are  then  suspended  until  incubation  takes  place.     The  yol-k, 
which  at  first  consists  of  a  mass  of  uniform  appearance,  grad- 
ually assumes  a  diversified  aspect.     Some  portions  become 
more  opaque    and  others  more  transparent ;  the  germinal 
vesicle,  whicn  was  in  the  midst  of  the  yolk,  rises  to  its  upper 
part  where  the  germ  is  to  be  formed.     Tiaese  early  changes 


DEVELOPMENT    OF    THE    YOUNG    WITHIN    THE    LGG.        Ill 

are  accompanied,  in  some  animals,  Dy  a  rotation  of  the  yolk 
within  the  egg,  as  may  be  distinctly  seen  in  some  of  the 
mollusks,  especially  in  the  snails. 

296.  At  the  same  time,  the  yolk  undergoes  a  peculiar 
process  of  segmentation.      It  is  first  divided   into   halves, 
forming   distinct  spheres,  which    are    again  regularly  sub- 
divided  into  two  more,  and   so  on,  till  the  whole  yolk  as- 
sumes the  appearance  of  a  mulberry,  each  of  the  spheres  of 
which  it  is  composed   having  in  its '  interior  a  transparent 
vesicle.      This  is  the  case   in   mammalia,  most  mollusks, 
worms,  &c.     In  .many  animals,  however,  as  in  the   naked 

*reptiles  and    fishes,*  this  segmentation  is  only  partial,  the 
divisions  of  the  yolk  not  extending  across  its  whole  mass. 

297.  But  whether  complete  or  partial,  this  process  leads 
to  the  formation  of  a  germ  comprising  the  whole  yolk,  or 
rising  above  it  as  a  disk-shaped  protuberance,  composed  of 
little  cells,  which  has  been  variously  designated  under  the 
names  of  germinative   disk,  proligerous  disk,  blastoderma, 
germinal  membrane.     In  this  case,  however,  that  portion  of 
the  yolk  which  has  undergone  less  obvious  changes  forms, 
nevertheless,  part  of  the  growing  germ.      The  disk  again 
gradually  enlarges,  until  it  embraces  the  whole,  or  nearly 
the  whole,  of  the  yolk. 

298.  At  this  early  epoch,  namely,  a  few  days,  and  some- 
times a  few  hours, 

after  development 
has  begun,  the 
germ  proper  con- 
sists of  a  single 
layer  composed  Fig.  102.  Fig.  103. 


*  In  the  Birds  and  higher  reptiles  we  find,  in  the  mature  egg,  a  peculiar 
organ,  called  cicatricula,  which  may.  nevertheless,  have  been  formed  by 
a  similar  proc  ?ss  before  it  was  laid. 


142  EMBRYOLOGY. 

of  very  minute  cells,  all  of  which  are  alike  in  appearance 
and  form,  (Fig.  102,  g.)  But  soon  after,  as  the  germ  increases 
in  thicRness,  several  layers  may  be  discerned,  in  vertebrated 
animals,  (Fig.  103,)  which  become  more  and  more  distinct. 

299.  The  upper  layer,  (s,)  in  which   are    subsequently 
formed  the  organs  of  animal  life,  namely,  the  nervous  sys- 
tem, the  muscles,  the  skeleton,  &c.,  (59,)  has  received  the 
name  of  serous  or  nervous  layer.     The  lower  layer,  (m,) 
which  gives  origin  to  the  organs  of  vegetative  life,  and  espe- 
cially to  the   intestines,  is  called   the  mucous  or  vegetative 
layer,  and  is  generally  composed  of  larger  cells  than  those 
of  the   upper  or   serous   layer.     Finally,  there    is   a   third 
layer,  (v,)  interposed  between  the  two  others,  giving  rise  to 
the  formation  of  blood  and  the  organs  of  circulation  ;  whence 
it  has  been  called  blood  layer,  or  vascular  layer. 

300.  From  the  manner  in  which  the  germ  is  modified,  we 
can  generally  distinguish,  at  a  very  early  epoch,  to  what  de- 
partment of  the  animal  kingdom  an  individual  is  to  belong. 
Thus,  in  the  Articulata,  the  germ  is  divided  into  segments, 

indicating  the  transverse  divisions 
of  the  body,  as,  for  example,  in  the 
embryo  of  the  crabs,  (Fig.  104.) 
The  germ  of  the  vertebrated  ani- 
mals, on  the  other  hand,  displays 
a  longitudinal  furrow,  which  marks 
Fig.  104.  Fig.  105.  the  pOSition  the  future  back-bone 
is  to  occupy,  (Fig.  105.) 

301.  The  development  of  this  furrow  is  highly  important, 
a>  indicating  the  plan  of  structure  of  vertebrated  animals  in 
general,  as  will  be  shown  by  the  following  figures,  which 
represent  vertical  sections  of  the  embryo  at  different  epochs.* 


*  In  these  figures,  the  egg  is  supposed  to  be  cut  down  through  the  mid- 
dle, so  that  mly  the  cut  edge  of  the  embryo  is  seen ;  whereas,  if  viewed 


DEVELOPMENT  OF  THE  YOUNG  WITHIN  THE  EGG.   113 

At  first  the  furrow  (Fig.  106,  Z>)  is  very  shallow,  and  a  lit- 


I 

Fig.  106.  Fig.  107.  Fig.  108. 

tie  transparent,  narrow  band  appears  under  it,  called  the 
primitive  stripe,  (a.)  The  walls  of  the  furrow  consist  of  two 
raissd  edges  formed  by  a  swelling  of  the  germ  along  both  sides 
of  the  primitive  stripe.  Gradually,  these  walls  grow  higher, 
and  we  perceive  that  their  summits  have  a  tendency  to  ap- 
proach each  other,  as  seen  in  Fig.  107 ;  at  last  they  meet 
and  unite  completely,  so  that  the  furrow  is  now  changed 
into  a  closed  canal,  (Fig.  108,  b.)  This  canal  is  soon  filled 
with  a  peculiar  liquid,  from  which  the  spinal  marrow  and 
brain  are  formed  at  a  later  period. 

302.  The   primitive  stripe  is  gradually  obliterated  by  a 
peculiar  organ  of  a  cartilaginous  nature,  the  dorsal  cord 
formed  in  the  lower  wall  of  the  dorsal  canal.     This  is  founo 
in  the  embryos  of  all  vertebrates,  and  is  the  representative 
of  the  back-bone.     In   the   mean  time,  the  margin  of  the 
germ  gradually  extends  farther  and  farther  over  the  yolk,  so 
as  finally  to  enclose  it  entirely,  and  form  another  cavity  in 
which  the  organs  of  vegetative  life  are  to  be   developed 
Thus  the  embryo  of  vertebrates  has  two  cavities,  namely, 
the  upper  one,  which  is  very  small,  containing  the  nervous 
system,  and  the  lower,  which  is  much  larger,  for  the  intes- 
tines, (161.) 

303.  In  all  classes  of  the  Animal  Kingdom,  the  embryo 
proper  rests  upon  the  yolk,  and  covers  it  like  a  cap.     Bui 
the  direction  by  which  its  edges  approach  each  other,  and 


from  above,  it  would  extend  over  the  yolk  in  every  direction,  and  the 
furrow  at  b,  of  Fig.  106,  would  appear  as  in  Fig.  105. 


144 


EMBRYOLOGY. 


Fig.  109. 


unite  tc  form  the  cavity  of  the  body,  is  very  unlike  in  dif 
ferent  animals ;  and  these  several  modes 

are  of  high  importance  in  classification. 
Among  the  Vertebrates,  the  embryo  lies 
with  its  face  or  ventral  surface  towards 
the  yolk,  (Fig.  109,)  and  thus  the  suture, 
or  line  at  which  the  edges  of  the  germ 
unite  to  enclose  the  yolk,  and  which  in 
the  mammals  forms  the  navel,  is  found 
in  front.  Another  suture  is  found  along 
the  back,  arising  from  the  actual  folding  upwards  of  the 
upper  surface  of  the  germ,  to  form  the  dorsal  cavity. 

304.  The  embryo  in  the  Articulata,  on  the  contrary,  lies 
with  its  back  upon  the  yolk,  as  seen  in  the  following  figure, 
which  represents  an  embryo  of  Podurella  ; 
consequently  the  yolk  enters  the  body  on 
that  side ;  and  the  suture,  which  in  the 
vertebrates  is  found  on  the  belly,  is  here 
found  on  the  back.  In  the  Cephalopoda 
the  yolk  communicates  with  the  lower 
side  of  the  body,  as  in  Vertebrates,  but 
there  is  no  dorsal  cavity  formed  in  them. 
In  the  other  Mollusks,  as  also  in  the  Worms,  there  is  this 
peculiarity,  that  the  whole  yolk  is  changed  at  the  beginning 
into  the  substance  of  the  embryo  ;  whilst  in  Vertebrates,  and 
the  higher  Articulates  and  Mollusks,  a  part  of  it  is  reserved, 
till  a  later  period,  to  be  used  for  the  nourishment  of  the  em- 
bryo.  Among  Radiata,  the  germ  is  formed  around  the  yolk, 
and  seems  to  surround  the  whole  of  it,  from  the  first.* 

805.  The  development  of  the  embryo  of  the  vertebrated 
animals  may  be  best  observed  in  the  eggs  of  fishes.     Being 


Fig.  110. 


*  These  facts  show  plainly  that  the  circumstance  of  embryos  arising 
from  the  whole  or  a  part  of  the  yolk  is  of  no  systematic  importance. 


DEVELOPMENT  OF  THE  YOUNG  WITHIN  THE  EGG.   145 

transparent,  they  do  not  require  to  be  cut  open,  and,  by 
sufficient  caution,  the  whole  series  of  embryonic  changes 
may  be  observed  upon  the  same  individual,  and  thus  the  suc- 
cession in  which  the  organs  appear  be  ascertained  with  pre- 
cision ;  whereas,  if  we  employ  the  eggs  of  birds,  which  are 
opaque,  we  aro  obliged  to  sacrifice  an  egg  for  each  obser- 
vation. 

306.  To  illustrate  these  general  views  as  to  the  develop-  \ 
nient  of  the  embryo,  we  will  briefly  describe  the  principal 
phases,  as  they  have  been  observed  in  the  White-fish  of  Eu- 
rope, which  belongs  to  the  salmon  family.  The  following 
magnified  sections  will  illustrate  this  development,  and  show 
the  period  at  which  the  different  organs  successively  appear. 


Fig.  111.  Fig.  112.  Fig.  Il 


307.  The  egg,  when  laid,  (Fig.  11  1,)  is  spherical,  about  the 
size  of  a  small  pea,  and  nearly  transparent.     It  has  no  albu- 
men, and  the  shell  membrane  is  so  closely  attached  to  the 
membrane  of  the  yolk,  that  they  cannot  be  distinguished. 
Oil-like  globules  are  scattered  through  the  mass  of  the  yolk, 
or  grouped  into  a  sort  of  disk,  under  which  lies  the  germina- 
tive  vesicle.     The  first  change  in  such  an  egg  occurs  a  few 
hours  after  it  has  been  laid,  when  the  shell  membrane  sepa- 
rates from  the  yolk  membrane,  in  consequence  of  the  ab- 
sorption of  a  quantity  of  water,  (Fig.  112,)  by   which  the 
egg  increases  in  size.     Between  the  shell   membrane  (s  m) 
and  the  yolk,  (y,)  there  is  now  a  considerable   transparent 
space,  which  corresponds,  in  some  respects,  to  the  albumen 
found  in  the  eggs  of  birds. 

308.  Soon  afterwards  we  see,  in  the  midst  of  the  oil-like 

13 


146 


EMBr>.y.  LOGY. 


globules,  a  swelling  in  the  shape  of  a  transparent  vesicle, 
(Fig.  113,  g,)  composed  of  very  delicate  cells.  This  is  tlm 
first  indication  of  the  germ.  This  swelling  rapidly  enlarges 
until  it  envelops  a  greai  part  of  the  yolk,  when  a  depression 


Fig.  114. 


Fig.  115. 


Fig.  116. 


is  formed  upon  it,  (Fig.  114.)  This  depression  becomes  by 
degrees  a  deep  furrow,  and  soon  after  a  second  furrow  ap- 
pears at  .right  angles  with  the  former,  so  that  the  germ  now 
presents  four  elevations,  (Fig.  115.)  The  subdivision  goes 
on  in  this  way,  during  the  second  and  third  days,  until  the 
germ  is  divided  into  numerous  little  spheres,  giving  the  sur- 
face the  appearance  of  a  mulberry,  (Fig,  116.)  This  ap- 
pearance, however,  does  not  long  continue  ;  at  the  end  of 
the  third  day,  the  fissures  again  disappear,  and  leave  no 
visible  traces.  After  this,  the  germ  continues  to  extend 
as  an  envelop  around  the  yolk,  which  it  at  last  entirely 
encloses. 

309.  On  the  tenth  day,  the  first  OM* lines  of  the  embryo 
begin  to  appear,  and  we  soon  distinguish  in  it  a  depression 
between  two  little  ridges,  whose  edge*  ^ustantly  approach 


Fig.  117.  Fig.  118.  Fig.  119. 

each  other  until  they  unite  and  form  a  canal,  ^Fig.  117,  £, 


DEVELOPMENT    OF    THE    YOUNG    WITHIN    THE    EGG.        147 

us  has  been  before  shown,  (Fig.  107.)  At  the  same  time, 
an  enlargement  at  one  end  of  the  furrow  is  observed.  This 
is  the  rudiment  of  the  head,  (Fig.  118,)  in  which  may  soon 
be  distinguished  traces  of  the  three  divisions  of  the  brain, 
(Fig.  119,)  corresponding  to  the  senses  of  sight,  (m,)  hear- 
ing, (e,)  and  smell,  (p.) 

310.  Towards  the  thirteenth  day,  we  see  a  transparent, 
cartilaginous  cord,  in  the  place  afterwards  occupied  by  the 
back-bone,  composed  of  large  cells,  on  which  transverse 


Fig.  120.  Fig.  121.  Fig.  122. 


divisions  are  successively  forming,  (Figs.  120,  121,  c.)  This 
is  the  dorsal  cord,  a  part  of  which,  as  we  have  before  seen,  is 
common  to  all  embryos  of  vertebrated  animals.  It  always 
precedes  the  formation  of  the  back-bone  ;  and  in  some 
fishes,  as  the  sturgeon,  this  cartilaginous  or  embryonic  state 
is  permanent  through  life,  and  no  true  back-bone  is  ever 
formed.  Soon  after,  the  first  rudiments  of  the  eye  appear 
in  the  form  of  a  fold  in  the  external  membrane  of  the  germ, 
in  which  the  crystalline  lens  (Fig.  121,  x)  is  afterwards 
formed.  At  the  same  time  we  see,  at  the  posterior  part 
of  the  head,  an  elliptical  vesicle,  which  is  the  rudiment  of  the 
ear.  At  this  period,  the  distinction  between  the  upper  and 
ihe  lower  layer  of  the  germ  is  best  traced ;  all  the  changes 
mentioned  above  appertaining  to  the  upper  layer. 

311.  After  the  seventeenth  day,  the  lower  layer  divides 
into  two  sheets,,  the  inferior  of  which  becomes  the  intestine 


148  EMBRYOLOGY. 

The  heart  shows  itself  about  the  same  time,  under  the  form 
of  a  simple  cavity,  (Fig.  121,  A,)  in  the  midst  of  a  mass 
of  cells  belonging  to  the  middle  or  vascular  layer.  As  soon 
as  the  cavity  of  the  heart  is  closed  in,  regular  motions  of 
contraction  and  expansion  are  perceived,  and  the  globules 
of  blood  are  seen  to  rise  and  fall  in  conformity  with  these 
motions. 

312.  There  is  as  yet,  however,  no  circulation.     It  is  not 
until  the  thirtieth  day  that  its  first  traces  are  manifest  in  the 
existence  of  two  currents,  one  running  towards  the  head,  the 
other  towards  the  trunk,  (Fig.  122,)  with  similar  returning 
currents.    At  this  time  the  liver  begins  to  be  formed.    Mean- 
while, the  embryo  gradually  disengages  itself,  at  both  ends, 
from  its  adherence  to  the  yolk  ;  the  tail  becomes  free,  and 
the  young  animal  moves  it  in  violent  jerks. 

313.  The  embryo,  although  still  enclosed  in  the  egg,  now 
unites  all   the   essential  conditions   for  the  exercise  of  the 
functions  of  animal  life.     It  has  a  brain,  an  intestine,  a  pul- 
sating heart  and  circulating  blood,  and  it  moves  its  tail  spon- 
taneously.   But  the  forms  of  the  organs  are  not  yet  complete 
nor  have  they  yet  acquired  the  precise  shape  that  character- 
izes the  class,  the  family,  the  genus,  and  the  species.     The 
young  White-fish  is  as  yet  only  a  vertebrate  animal  in  gen- 
eral, and  might  as  well  be  taken  for  the  embryo  of  a  frog. 

314.  Towards  the  close  of  the  embryonic  period,  after  the 
fortieth   day,   the    embryo  acquires  a  more  definite  shape. 
The  head  is  more  completely  separated  from  the  yolk,  the 
jaws  protrude,  and  the  nostrils  approach  nearer  and  nearer  to 
the  end  of  the  snout;  divisions  are  formed  in  the  fin  which 
surrounds  the  body  ;  the  anterior  limbs,  which  were  indicated 
only  by  a  small  protuberance,  assume  the  shape  of  fins  ;  and 
finally,  the  openings  of  the  gills  appear,  one  after  the  other 
so  that  we  cannot  now  fail  to  recognize  the  type  of  fishes. 

315.  In  this  state,  the  young  white-fish  escapes  from  the 


DEVELOPMENT    OF    THE    YOUNG    WITHIN    THE    EGG. 


tgg,  about  the  sixtieth  day  after  it  is  laid,  (Fig.  123,)  but 
its  development  is^still 
incomplete.  The  out- 
lines are  yet  too  indis- 
tinct to  indicate  the 
genus  and  the  species  F{g>  123. 

to  which   the   fish   be- 

loi.gs  ;  a*  most  we  distinguish  its  order  only.  The  opercula 
or  gill-covers  are  not  formed;  the  tee.h  are  wanting;  the 
fins  have  as  yet  no  rays  ;  the  mouth  is  underneath,  and  it 
is  some  time  before  it  assumes  its  final  position  at  the  most 
projecting  point  of  the  head.  The  remainder  of  the  yolk  is 
suspended  from  the  belly,  in  the  form  of  a  large  bladder,  but 
it  daily  diminishes  in  si2e,  until  it  is  at  length  completely  taken 
into  the  animal,  (304.)  The  duration  of  these  metamorphoses 
varies  extremely  in  different  fishes  ;  some  accomplish  it  in  the 
course  of  a  few  days,  while  in  others,  months  are  required. 


315  a.  In  frogs  and  all  the  naked  reptiles,  the  development  is  very 
similar  to  that  of  fishes.  It  is  somewhat  different  in  the  scaly  rep- 
tiles, (snakes,  lizards,  and  turtles,)  which  have  peculiar  membranes 
surrounding  and  protecting  the  embryo  during  its  growth.  From 
one  of  these  envelopes,  the  allantoTs,  (Fig.  125,  a,)  is  derived  theii 
common  name  of  Attantoldian  Vertebrates,  in  opposition  to  the  naked 
reptiles  and  fishes,  which  are  called  Anallantoldian. 

315  6.  The  AllantoTdian  Vertebrates  differ  from  each  other  in 
several  essential  peculiarities.  Among  Birds,  as  well  as  in  the  scaly 


Fig.  124.  Fig.  125. 

;  we  find  at  a  certain  epoch,  when  the  embryo  is  already  dis- 
13* 


150  EMBRYOLOGY. 

316.  As  a  general  fact,  it  should  be  further  stated,  that 
the  envelopes  which  protect  the  egg,  and  also  the  embryo, 
are  the  more  numerous  and  complicated  as  animals  belong 
to  a  higher  class,  and  produce  a  smaller  number  of  eggs. 
This  is  particularly  evident  when  contrasting  the  innumer- 
able eggs  of  fishes,  discharged  almost  without  protection 


engaging  itself  from  the  yolk,  a  fold  rising  around  the  body  from  the 
upper  layer  of  the  germ,  so  as  to  present,  in  a  longitudinal  section, 
two  prominent  walls,  (Fig.  124,  x  x.)  These  walls,  converging  from 
all  sides  upwards,  ris3  gradually  till  they  unite  above  the  middle  of 
the  back,  (Fig.  125.)  When  the  junction  is  effected,  which  in  the 
hen's  egg  takes  place  in  the  course  of  the  fourth  day*  a  cavity  is 
formed  between  the  back  of  the  embryo  (Fig.  126,  e)  and  the  new 
membrane,  whose  walls  are  called  the  amnios.  This  cavity  becomes 
filled  with  a  peculiar  liquid,  the  amniotic  icater. 

315  c.  Soon  after  the  embryo  has  been  enclosed  in  the  amnios,  a 
shallow  pouch  forms  from  the  mucous  layer,  below  the  posterior  ex- 
tremity of  the  embryo,  between  the  tail  and  the  vitelline  mass.  This 
pouch,  at  first  a  simple  little  sinus,  (Fig.  125,  a,)  grows  larger  and 
larger,  till  it  forms  an  extensive  sac,  the  allantois,  turning  backwards 
and  upwards,  so  as  completely  to  separate  the  two  plates  of  the  am- 
IUOF,  (Fig.  126,  a.)  and  finally  enclosing  the  whole  embryo,  with  us 


Fig.  126. 

amnios,  in  another  large  sac.  The  tubular  part  of  this  sac,  which  is 
nearest  the  embryo,  is  at  last  transformed  into  the  urinary  bladder. 
The  heart  (A)  is  already  very  large,  with  mniute  arterial  threads 


DEVELOPMENT    OF    THE    YOUNG    WITHIN    THE    EGG.       151 

into  the  water,  with  the  well-protected  eggs  of  birds,  and 
still  more  with  the  growth  of  young  mammals  within  the 
body  of  the  mother. 

317.  But  neither  in  fishes,  nor  in  reptiles,  nor  in  birds, 
does  the  vitelline  membrane,  or  any  other  envelope  of  the  egg, 
take  any  part  in  the  growth  of  the  embryo ;  while  on  the 


Fig.  127. 


Fig.  128. 


passing  off  from  it.     At  this  period  there  exist  true  gills  upon  the 
sides  of  the  neck,  and  a  branchial  respiration  goes  on. 

315  d.  The  development  of 
mammals  exhibits  the  folio-wing 
peculiarities.  The  egg  is  ex- 
ceedingly minute,  almost  micro- 
scopic, although  composed  of  the 
same  essential  elements  as  those 
of  the  lower  animals.*  The  vitel- 
line membrane,  called  chorion,  in 

this  class  of  animals,  is  comparatively  thicker,  (Fig.  127,  v,)  always 
soft,  surrounded  by  peculiar  cells,  being  a  kind  of  albumen.  The 
chorion  soon  grows  proportionally  larger  than  the  vitelline  sphere 
itself,  (Fig.  128,  y,)  so  as  no  longer  to  invest  it  directly,  being  sepa- 
rated from  it  by  an  empty  space,  (&.)  The  germ  is  formed  in  the 
same  position  as  in  the  other  classes  of  Vertebrates,  namely,  at  the  top 
of  the  vitellus,  (Fig. 
129  ;)  and  here  also 
two  luyers  may  be 
distinguished,  the  up- 
per or  serous  layer,  (*,) 
and  the  lower  or  mu- 
cous layer,  (m.)  As 
it  gradually  enlarges, 
the  surface  of  the 
chorion  becomes  cov- 
ered with  little  fringes,  which,  at  a  later  epoch,  will  be  attached  to 
the  mother  by  means  of  similar  fringes  arising  from  the  walls  of 
the  matrix,  or  organ  which  contains  the  embryo. 

315  e.  The  pmbryo  itself  undergoes,  within  the  cnorion   changes 


Fig.  129. 


Fig.  130. 


152 


EMBRYOLOGY. 


contrary,  in  the  mammals,  the  chorion,  which  cor  responds 
to  the  vitelline  membrane,  is  vivified,  and  finally  becomes 
attached  to  the  maternal  body,  thus  establishing  a  direct  con- 
nection between  the  young  and  the  mother ;  a  connection 
which  is  again  renewed  in  another  mode,  after  birth,  by  the 
^rocess  of  nursing. 


similar  to  those  described  in   birds :    its  body  and  its  organs   are 
formed  in  the  same  way ;  an  amnios  encloses  it,  and  an  allantolfs 
grows  out  of  the  lower  extremity  of  the  little  animal.    As  soon  as  the 
allantoYs  has  surrounded  the  embryo,  its  blood  vessels  become  more 
and  more  numerous,  so  as  to  extend  into  the 
fringes  of  the  chorion,  (Fig.  131,  pe;)  while, 
on  the  other  hand,  similar  vessels  from  the 
mother    extend    into    the     corresponding 
fringes  of  the  matrix,  (p  m,)  but  without 
directly  communicating  with  those  of  the 
ehorisn.     These  two  sorts  of  fringes  soon 
become  interwoven,  SD  as  to  form  an  intri- 
cate organ  filled  with  blood,  called  the  pla- 
centa, to  which  the  embryo  remains  sus- 
pended until  birth. 

315 /.  From  the  fact  above  stated,  it  is  clear  that  there  are  three 
modifications  of  embryonic  development  among  vertebrated  animals, 
namely,  that  of  fishes  and  naked  reptiles,  that  of  scaly  reptiles  and 
birds,  and  that  of  the  mammals,  which  display  a  gradation  of  more  and 
more  complicated  adaptation,  in  fishes  and  the  naked  reptiles,  the 
germ  simply  encloses  the  yolk,  and  the  embryo  rises  and  grows  from 
its  upper  part.  In  the  scaly  reptiles  and  birds  there  is,  besides,  an 
amnios  arising  from  tie  peripheric  part  of  the  embryo  and  an  allantoYs 
growing  out  of  lie  iower  cavity,  both  enclosing  and  protecting  the 
germ. 


Fig.  131. 


ITS    ZOOLOGICAL    IMPORTANCE.  153 

SECTION  III. 

ZOOLOGICAL    IMPORTANCE    OF    EMBRYOLOGY. 

318.  As  a  general  result  of  the  observations  which  ha,ve 
been  mide,  up  to  this  time,  on  the  embryology  of  the  various 
classes  of  the  Animal  Kingdom,  especially  of  the  veite 
brates,  it  may  be  said,  that  the  organs  of  the  body  are  suc- 
cessively fcrmed  in  the  order  of  their  organic  importance, 
the  most  essential  being  always  the  earliest  to  appear,     in 
accordance  with  this  law,  the  organs  of  vegetative  life,  the 
intestines  and  their  appurtenances,  make  their  appearance 
subsequently  to  those  of  animal   life,  such   as  the  nervous 
system,  the  skeleton,  &c. ;  and  these,  in  turn,  are  preceded 
by  the  more  general  phenomena  belonging  to  the  animal  as 
such. 

319.  Thus  we  have  seen  that,  in  the  fish,  the  first  changes 
relate  to  the  segmentation  of  the  yolk  and  the  formation  of 
the  germ,  which  is  a  process  common  to  all  classes  of  ani- 
mals.    It  is  not  until  a  subsequent  period  that  we  trace  the 
dorsal  furrow,  which  indicates  that  the  formiiig  animaj  will 
have  a  double  cavity,  and  consequently  belong  to  the  di\lsion 
of  the  vertebrates;  an  indication  afterwards  fully  confirmed 
by  the  successive  appearance  of  the  brain  and  the  organs 
of  sense.     Later  still,  the  intestine  is  formed,  the  limbs  be- 
come evident,  and  the  organs  of  respiration  acquire  their 
definite  form,  thus  enabling  us  to  distinguish  with  certainty 
the  class  to  which  the  animal  belongs.     Finally,  after  the 
egg  is  hatched,  the  peculiarities  of  the  teeth,  and  the  shape 
of  the  extremit  es,  mark  the  genus  and  species. 

320.  Hence   the  embryos  of  different  animals  resemble 
each   otner  more    strongly  when   examined   in   the  earlier 
stages  of  the!  r  growth      We  have  already  stated  that,  during 


154  EMBRYOLOGY. 

almost  the  whole  period  of  embryonic  life,  the  young  fish 
and  the  young  frog  scarcely  differ  at  all,  (313  :)  so  it  is  also 
with  the  young  snake  compared  with  the  embryo  bird.  The 
embryo  of  the  crab,  again,  is  scarcely  to  be  distinguished 
from  that  of  the  insect;  and  if  we  go  still  further  back  in 
the  history  of  development,  we  come  to  a  period  when  n3 
appreciable  difference  whatever  is  to  be  discovered  between 
the  embryos  of  the  various  departments.  The  embryo  of 
the  snail,  when  the  germ  begins  to  show  itself,  is  nearly  the 
same  as  that  of  a  fish  or  a  crab.  All  that  can  be  predicted 
at  this  period  is,  that  the  germ  which  is  unfolding  itself 
will  become  an  animal ;  the  class  and  the  group  are  not  yet 
indicated. 

321.  After  this  account  of  the  history  of  the  development 
of  the  egg,  the  importance  of  Embryology  to  the  study  of 
systematic  Zoology  cannot  be  questioned.     For  evidently,  if 
the  formation  of  the  organs  in  the  embryo  takes  place  in  an 
order  corresponding  to  their  importance,  this  succession  must 
of  itself  furnish  a  criterion  of  their  relative  value  in  classifi- 
cation.    Thus,  those  peculiarities  that  first  appear  should  be 
considered  of  higher  value  than  those  that  appear  later.     In 
this  respect,  the  division  of  the  Animal  Kingdom  into  four 
types,  the  Vertebrates,  the  Articulates,  the  Mollusks,  and  the 
Radiates,  corresponds  perfectly  with  the  gradations  displayed 
b/  Embryology. 

322.  This  classification,  as  has  been  already  shown,  (61,) 
is  founded  essentially  on  the  organs  of  animal  life,  the  ner- 
vous system  and  the  parts  belonging  thereto,  as  found  in  the 
perfect  animal.     Now,  it  results  from   the  above  account, 
that  in  most  animals  the  organs  of  animal  life  are  precisely 
those  that  are  earliest  formed  in  the  embryo ;  whereas  those 
of  vegetative  life,  on   which    is   founded   the  division   into 
classes,  orders,  and  families,  such  as  the  heart,  the  respirator" 
apparatus,  and  the  jaws,  are  not  distinctly  formed  until  after- 


ITS>    ZOOLOGICAL    IMPORTANCE.  155 

wards.  Therefore  a  classification,  to  be  true  and  natural 
must  accord  with  the  succession  of  organs  in  the  embryonic 
development.  This  coincidence,  while  it  corroborates  the 
anatomical  principles  of  Cuvier's  classification  of  the  Animal 
Kingdom,  furnishes  us  with  new  proof  that  there  is  a  general 
plan  displayed  in  every  kind  of  development. 

323.  Combining  these  two  points  of  view,  that  of  Embry 
ology  with  that  of  Anatomy,  the  four  divisions  of  the  Anima) 
Kingdom  may  be  represented  by  the  four  figures  which  are 
to  be  found,  at  the  centre  of  the  diagram,  at  the  beginning 
of  the  volume. 

324.  The  type  of  Vertebrates,  having  two  cavities,  one 
above  the  other,  the  former  destined  to  receive  the  nervous 
system,  and  the  latter,  which  is  of  a  larger  size,  for  the  intes- 
tines, is  represented  by  a  double  crescent  united  at  the  cen- 
tre, and  closing  above,  as  well  as  below. 

325.  The  type  of  Articulata,  having  bu^t  one  cavity,  grow- 
ing from  below  upwards,  and  the  nervous  system  forming 
a  series  of  ganglions,  placed  below  the  intestine,  is  repre- 
sented  by  a  single    crescent,  with   the  horns  directed  up- 
wards. 

326.  The  type  of  Mollusks  having  also  but  one  cavity,  the 
nervous  system  being  a  simple  ring  around  the  oesophagus, 
with  ganglions  above  and  below,  from  which  threads  go  off 
to  all  parts*  is  represented  by  a  single  crescent  with  the 
hoins  turned  downwards. 

327.  Finally,  the  type  of  Radiata,  the  radiating  form  of 
which  is  seen  even  in  the  youngest  individuals,  is  represented 
by  a  star. 


CHAPTER    ELEVENTH. 

PECULIAR    MODES    OF    REPRODUCTION. 
SECTION   L 

GEM  \IIPAROTTS    AND    FISSIPAROUS    REPRODUCTION. 

328.  WE  have  shown  in  the  preceding  chapter,  that  ovuU- 
(ion,  and  the  development  of  embryos  from  eggs,  is  common 
to  all  classes  of  animals,  and  must  be  considered  as  the  great 
process  for  the  reproduction  of  species.     Two  other  modes 
of  propagation,  applying,  however,  to  only  a  limited  number 
of  animals,  remain  to  be  mentioned,  namely,  gemmiparous 
reproduction,  or  multiplication  by  means  of  buds,  and  fissip- 
arous   reproduction,  or   propagation  by  division ;   and    also 
some  still  more  extraordinary  modifications  yet  involved  in 
much  obscurity. 

329.  Reproduction  by  buds  occurs  among  the  polyps,  me- 

dusae, and  some  of  the  infusoria.  .On  the  stalk, 
or  even  on  the  body  of  the  Hydra,  (Fig.  132,) 
and  of  many  infusoria,  there  are  formed 
buds,  like  those  of  plants.  On  close  exam- 
ination they  are  found  to  be  young  animals 
at  first  very  imperfectly  formed,  and  commu* 
nicating  at  the  base  with  the  parent  body, 
from  which  they  derive  their  nourishment.  By 

T        1  ^*? 

degrees,  the  animal  is  developed  ;    in   most 
cases,  the   tube  by  which  it  is  connected  with  the   parent 


GEMMIPAROUS    AND    FISSIPAROUS    REPRODUCTION.         157 


withers  away,  and  the  animal  is  thus  detached  and  becomes 
independent.  Others  remain  through  life  united  to  the  parent 
stalk,  and,  in  this  respect,  present  a  more  striking  analogy  to 
the  buds  of  plants.  But  in  the  polyps,  as  in  trees,  budding 
is  only  an  accessory  mode  of  reproduction,  which  pre- 
supposes a  trunk  already  existing,  originally  the  product  ol 
ovulation. 

330.  Reproduction  ly  division,  or  fissiparous  reproduction 
is  still  more  extraordinary  ;  it  takes  place  only  in  polyps  and 
some  infusoria.  A  cleft  or  fissure  at  some  part  of  the  body 
takes  place,  very  slight  at  first, 
but  constantly  increasing  in 
depth,  so  as  to  become  a  deep 
furrow,  like  that  observed  in  the 
yolk,  at  the  beginning  of  embry- 
onic development ;  at  the  same 
time  the  contained  organs  are  di- 
vided and  become  double,  and  thus  two  individuals  are  formed 
of  one,  so  similar  to  each  other  that  it  is  impossible  to  say  which 
is  the  parent  and  which  the  offspring.  The  division  takes  place 
sometimes  vertically,  as,  for  example,  in  Vorticella,  (Fig, 
133,)  and  in  some  Polyps,  (Fig.  134,)  and  sometimes  trans- 


Fig.  133. 


Fig.  134. 

versely.     In   some  Infusoria,  the  Paramecia,  for  instance, 

this  division  occurs  as  often  as  three  or  four  times  in  a  day. 

331.  In  consequence  of  this  same  faculty,  many  animals 

are  able  to  reproduce  various  parts  of  their  bodies  when 

accidentally  lost.     It  is  well  known  that  crabs  and  spiders, 

on  losing  a  limb,  acquire  a  new  one.     The  same  happens 

with  t  le  ai  ms  of  the  star-fishes.     The  tail  of  a  lizard  is  also 

14 


158 


REPRODUCTION 


readily  reproduced.     Salamanders  even   possess  the  facu'ty 
of  reproducing  parts  of  the  head,  including  the  eye  with  al) 
its  complicated  structure.     Something  similar  takes  place  in 
our  own  bodies,  when  a  new  skin  is  formed  over  a  wound 
or  when  a  broken  bone  is  reunited. 

332.  In  some  of  the  lower  animals,  this  power  of  repara- 
tion is  carried  much  farther,  and  applies  to  the  whole  body, 
so  as  closely  to  imitate  fissiparous  reproduction.     If  an  earth- 
worm, or  a  fresh-water  polyp,  be  divided  into  several  pieces, 
the  injury  is  soon  repaired,  each  fragment  speedily  becoming 
a  perfect  animal.     Something  like  this  reparative  faculty  is 
seen  in  the  vegetable  kingdom,  as  well  as  the  animal.     A 
willow  branch,  planted  in  a  moist  soil,  throws  out  roots  below 
and  branches  above  ;  and   thus,  after  a  time,  assumes  the 
shape  of  a  perfect  tree. 

333.  These  various  modes  of  reproduction  do  not  exclude 
each  other.     All  animals  which  propagate  by  gemmiparous 
or  fissiparous  reproduction  also  lay  eggs.     Thus  the  fresh- 
water polyps  (Hydra)  propagate  both  by  eggs  and  by  buds. 
In  Vorticella,  according  to  Ehrenberg,  all  three  jflodes  are 
found  ;  it  is  propagated   by  eggs,  by  buds,  and   by  division. 
Ovulation,  however,  is,  the  most  con  non  mode  of  reproduc- 
tion ,  the  other  modes,  and  also  alternate  reproduction,  are 
only  additional  means  employed  by  Nature  to  secure  the  per- 
petuation of  the  species. 

••-• 

SECTION    II. 

ALTERNATE    AND    EQUIVOCAL    REPRODUCTION. 

334.  It  is  a  matter  of  common  observation,  that  individuals 
of  the  same  species  have  the  same  general  appearance,  1  y 
which  theii   peciliar  organization  is  indicated.     The  Iran* 


ALTERNATE  AND  EQUIVOCAL  REPRODUCTION.     159 

mission  of  these  characteristics,  from  one  generation  to  the 
next,  is  justly  considered  as  one  of  the  great  laws  of  the 
Animal  and  Vegetable  Kingdoms.  It  is,  indeed,  one  of  the 
points  on  which  the  definition  of  species  is  generally  founded. 
We  would,  however,  unhesitatingly  adopt  the  new  definition 
of  Dr.  S,  G.  Morton,  who  defines  species  to  be  "  primordial 
organic  forms." 

335.  But  it  does  not  follow  that  animals  must  resemble 
their  parents  in  every  condition,  and  at  every  epoch  of  their 
existence.     On  the  contrary,  as  we  have  seen,  this  resem- 
blance  is  very  faint,  in   most  species,  at  birth  ;  and  some, 
such   as    the    caterpillar   and    the    tadpole,    undergo    com- 
plete metamorphoses  before  attaining  their  final  shape  as  the 
butterfly  and  frog.     Nevertheless,  we  do  not  hesitate  to  refer 
the  tadpole  and  the  frog  to  the  same  species ;  and  so  with  the 
caterpillar  and  the  butterfly  ;  because  we  know  that  there  is  the 
same  individual  observed  in  different  stages  of  development. 

336.  There  is,  also,  another  series  of  cases,  in  which  the 
offspring  not  only  do  not  resemble  the  parent  at  birth,  but, 
moreover,  remain  different  during  their  whole  life,  so  that 
their  relationship  is  not  apparent  until  a  succeeding  genera- 
tion.    The  son  does  not  resemble  the  father,  but  the  grand- 
father ;  and   in  some  cases  the  resemblance  reappears  only 
at  the  fourth  or  fifth  generation,  and  even  later.     This  sin- 
gular mode  of  reproduction  has  received  the  name  of  alter- 
nate generation.     The   phenomena  attending  it  have  been 
of  late  the  object  of  numerous  scientific  researches,  which 
are  the  more  deserving  of  our  attention,  as  they  furnish  a 
solution  to  several  problems  alike  interesting  in  a  zoological 
and  in  a  philosophical  point  of  view. 

337.  Alternate  generation  was  first  observed  among  tl  e 
Salpae.     These  are  marine  mollusks,  without  shells,  belong- 
ing to  the  family  Tunicata.     They  are  distinguished  by  ihu 
curious  peculiarity  of  being  united  together  in   considerable 
numbers   so  as  to  form  long  chains,  which  float   in  the  sea. 


160  REPRODUCTION. 

he  mouth,  (m,)  however,  being  free  in  each,  (Fig.  135) 


Fig.  135. 


Fig.  136. 


The  individuals  thus  joined  in  floating  colonies  produce  eggs ; 
but  in  each  animal  there  is  generally  but  one  egg  formed, 
which  is  developed  in  the  body  of  the  parent,  and  from 
which  is  hatched  a  little  mollusk,  (Fig.  136,)  which  remains 
solitary,  and  differs  in  many  respects  from  the  parent.  This 
little  animal,  on  the  other  hand,  does  not  produce  eggs,  but 
propagates  by  a  kind  of  budding,  which  gives  rise  to  chains 
already  seen  within  the  body  of  their  parent,  (a,)  and  these 
again  bring  forth  solitary  individuals,  &c. 

338.  In  some  parasitic  worms,  alternate  generation  is 
accompanied  by  still  more  extraordinary  phenomena,  as  is 
shown  by  the  late  discoveries  of  the  Danish  naturalist,  Steen- 
strup.  Among  the  numerous  animals  which  inhabit  stagnant 
pools,  in  which  fresh-water  shells,  particularly  Lymnea  and 
Paludina,  are  found,  there  is  a  small  worm, 
know  to  naturalists  under  the  name  of  Cer- 
caria,  (Fig.  137.)  When  examined  with 
a  lens,  it  looks  much  like  a  tadpole,  with  a 
long  tail,  a  triangular  head,  and  a  large 
sucker  (a)  in  the  middle  of  the  body.  Va- 
rious viscera  appear  within,  and,  among 
others,  a  very  distinct  forked  cord,  (c.,) 
which  embraces  the  sucker,  and  which  is 
thought  to  be  the  liver. 

339.  If  we  watch  these  worms,  which 
always  abound  in  company  with  the  shells 
mentioned,  we  find  them  after  a  while  attaching  themselves, 
by  mear.s  of  'heir  sucker,  to  the  bodies  of  the  mollusks.  When 


Fig.  137. 


ALTERNATE    AND    EQUIVOCAL    REPRODUCTION. 


161 


Fig.  138. 


The  fol 


fix  3d  they  soon  undergo  considerable  alteration.  The  tail, 
which  was  previously  employed  for  locomotion,  is  now  use- 
less, falls  off,  and  the  animal  surrounds  itself  with  a  .ttucous 
substance,  in  which  it  remains  nearly  motionless, 
like  the  caterpillar  on  its  transformation  into  the 
Pupa.  If,  however,  after  some  time,  we  remove 
the  litile  animal  from  its  retreat,  we  find  it  to  be 
no  longer  a  Cercaria,  but  an  intestinal  worm, 
called  Distoma,  having  the  shape  of  Fig.  138, 
with  wo  suckers.  The  Distoma,  therefore,  is 
only  a  particular  state  of  the  Cercaria,  or,  rather, 
the  Cercaria  is  only  the  larva  of  the  Distoma. 

340.  What  now  is  the  origin  of  the  Cercaria  ? 
lowing  are  the  results  of  the  latest  researches  on  this  point. 
At  certain  periods  of  the  year,  we  find  in  the  viscera  of  the 
Limnea  (one  of  the  most  common  fresh-water  mollusks)  a 
quantity  of  little  worms  of  an  elongated  form, 
v  ith  a  well  marked  head,  and   two  posterior 
projections  like  limbs,  (Fig.  139.)     On  examin- 
ing these  worms  attentively,  under  the  micro- 
scope, we   discover  that  the  cavity  of    their 
body  is  filled  by  a  mass  of  other  little  worms, 
which   a   practised    eye    easily  recognizes  as 
young  CercariaB,  the  tail  and  the  characteristic 
furcated  organ  (a)  within   it  being  distinctly  visible,  (Fig. 
140.)     These  little  embryos 
increase  in  size,  distending 
the    worm   which   contains 
them,  and  which  seemingly 
has  no  other  office  than  to 
protect  and  forward  the  de-  Fig.  140. 

ve\opment     of    the     young 

Cercaria.     It  is,  as  it  were,  their    living  envelop.     On  this 
account,  i«  has  been  called  the  nurse. 
14* 


Fig.  139. 


162  REPRODUCTION. 

341.  When  they  have  reached  a  certain  size,  the  young 
Cercurioe  lea~'e  the  body  of  the  nurse,  and  move  freely  in 
the  abdornina    cavity  of  the  mollusks,  or  escape  from  it  intc 
the  water,  to   fix  themselves,  in  their  turn,  to  the  body  of 
another  rnollusk,  and  begin  their  transformations  anew. 

342.  But  this  is  not  the  end  of  the  series.     The  nurses  of 

the  Cercaria  are  themselves  the  offspring  of  little 
worms  of  yet  another  kind.  At  certain  seasons, 
we  find  in  the  viscera  of  the  Limnea,  worms 
somewhat  like  the  nurses  of  Cercaria  in  shape, 
(Fig.  141,)  but  rather  longer,  more  slender,  and 
having  a  much  more  elongated  stomach,  (5.) 
These  worms  contain,  in  the  hinder  part  of  the 
body,  little  embryos,  («,)  which  are  the  young 
nurses,  like  Figures  139,  140.  This  generation 
has  received  the  name  of  grand-nurses. 

343.  Supposing  these  grand-nurses  to  be  the  immediate 
offspring  of  the  Distoma,  (Fig.  138,)  as  is  probable,  we  have 
thus  a  quadruple    series  of  generation.     Four    generations 
and  one  metamorphosis  are  required  to  evolve  the  perfect 
animal  ;  in  other  words,  the  parent  finds  no  resemblance  to 
himself  in  any  of  his  progeny,  until  he  comes  down  to  the 
great-grandson. 

344.  Among  the  Aphides,  or  plant-lice,  the  number  of 
generations  is  still  greater.     The  first  generation,  which  is 
produced  from  eggs,  soon   undergoes    metamorphoses,  and 
then  gives  birth  to  a  second  generation,  which  is  followed  by 
a  third,  and  so  on  ;  so  that  it  is  sometimes  the  eighth  or 
ninth  generation  before  the  perfect  animals  appear  as  males 
and  females,  the  sexes  being  then  for  the  first  time  distinct, 
and  the  males  provided  with  wings.     The  females  lay  eggs, 
which  are  hatched  the  following  year,  to  repeat  the  same 
succession.     Each  generation  is  an  additional  step  towards 
the  prefect  state  ;  and,  as  each  member  of  the  succession  is 


ALTERNATE  AND  EQUIVOCAL  REPRODUCTION.     163 

an  incomplete  animal,  we  cannot  better  explain  their  office, 
than  by  considering  them  analogous  to  the  larvae  of  the 
Cercaria,  that  is,  as  nurses.* 

345.  The  development  of  the  Medusse  is  not  less  instruc- 
tive.    According  to  the  observat  ons  of  Sars.,  a  Norwegian 
naturalist,  the    Medusa   brings   forth   living   young,  which, 
after  having   burst   the   covering   of  the  egg,  swim   about 
freely  for  some  time  in  the    body  of  the   mother.     When 
born,  these  animals  have   no  resemblance  whatever  to  the 
perfect  Medusa.     They  are   little    cylindrical  bodies,  (Fig. 
142,  a,)  much  resembling  infusoria,  and,  like  them,  covered 
with  minute  cilia,  by  means  of  which  they  swim  with  much 
activity. 

346.  After  swimming  about  freely  in  the  water  for  some 
days,  the  little  animal  fixes  itself  by  one  extremity,  (Fig. 
142,  e.)     At  the  opposite  extremity  a  depression  is  gradu- 

*  There  is  a  certain  analogy  between  the  larvse  of  the  plant-louse 
(Aphis)  and  the  neuters  or  working  ants  and  bees.  This  analogy  has 
given  rise  to  various  speculations,  and,  among  others,  to  the  following 
theory,  which  is  not  without  interest.  The  end  and  aim  of  all  alternate 
generation,  it  is  said,  is  to  favor  the  development  of  the  species  in  its 
progress  towards  the  perfect  state.  Among  the  plant-lice,  as  among  all 
the  nurses,  this  end  is  accomplished  by  means  of  the  body  of  the  nurse. 
Now,  a  similar  end  is  accomplished  by  the  working  ants  and  bees,  only, 
instead  of  being  performed  as  an  organic  function,  it  is  turned  into  an 
outward  activity,  which  makes  them  instinctively  watch  over  the  new  gen- 
eration, nurse  and  take  care  of  it.  It  is  no  longer  the  body  of  the  nurse, 
but  its  own  instincts,  which  become  the  instrument  of  the  development. 
This  seems  to  receive  confirmation  from  the  fact  that  the  working  bees, 
like  the  plant-lice,  are  barren  females.  The  attributes  of  their  sex,  in 
both,  seem  to  consist  only  in  their  solicitude  for  the  welfare  of  the  new 
generation,  of  which  they  are  the  natural  guardians,  but  not  the  parents. 
The  task  of  bringing  forth  young  is  confided  to  other  individuals,  -o  the 
jjueen  among  the  bees,  and  to  the  female  of  the  last  generation  among 
the  plant-lice.  Thus  the  barrenness  of  the  working  bees,  which  seems 
an  anomaly  as  long  as  we  consider  them  complete  animals,  receives 
a  very  natural  explanation  so  soon  as  we  look  upon  them  merely  as 
nurses 


164  REPRODUCTION. 

ally  formed   the  four  corners  (b  f)  become  elongated,  and 
by   degrees,  are  transformed    into    tentacles,    (c.)  •    Tnese 


0     CO 

2 


g          Fig.  142.  k 

tentacles  rapidly  multiply,  until  the  whole  of  the  upper 
margin  is  covered  with  them,  (g.)  Then  transverse 
wrinkles  are  seen  on  the  body,  at  regular  distances,  ap- 
pearing first  above  and  extending  downwards.  These 
wrinkles,  which  are  at  first  very  slight,  grow  deeper  and 
deeper,  and,  at  the  same  time,  the  edge  of  each  segment 
begins  to  be  serrated,  so  that  the  animal  presents  the  ap- 
pearance of  a  pine  cone,  surmounted  by  a  tuft  of  tentacles, 
(h  ;)  whence  the  name  of  Strobila,  which  was  originally 
given  to  it,  before  it  was  known  to  be  only  a  transient  state 
of  the  jelly-fish.  The  separation  constantly  goes  on,  until  at 
last  the  divisions  are  united  by  only  a  very  slender  axis,  and 
resemble  a  pile  of  cups  placed  within  each  other,  (i.) 
The  divisions  are  now  ready  for  separation ;  the  upper  ring 
first  disengages  itself,  and  then  the  others  in  succession.* 
Each  segment  (d)  then  continues  its  development  by  itse'f, 
until  it  becomes  a  complete  Medusa,  (k ;)  while,  according 
to  recent  researches5  the  basis  or  stalk  remains  and  pro- 
duces a  new  colony. 

347.    It  is  thus,  by  a  series  of  metamorphoses,  that  the 
little  animal  which,  on  leaving  the  egg,  has  the  form  of  the 

*  These  free  segments  have  been  described  as  peculiar  animals,  ui  der 
he  narie  of  Ephyra. 


ALTERNATE    AND    EQUIVOCAL    REPRODUCTION.  165 

Infusoria,  passes  in  succession  through  all  the  phases  we 
have  described.  But  the  remarkable  point  in  these  meta- 
morp. loses  is,  that  what  was  at  first  a  single  individual  is 
thus  transformed,  by  transverse  division,  into  a  number  of 
entirely  distinct  animals,  which  is  not  the  case  in  ordinary 
metamorphoses.  Moreover,  the  upper  segment  does  not 
follow  the  others  in  their  development.  Its  office  seems  to 
be  accomplished  so  soon  as  the  other  segments  begin  to  be 
independent,  being  intended  merely  to  favor  their  develop- 
ment, by  securing  and  preparing  the  substances  necessary 
to  their  growth.  In  this  respect,  it  resembles  the  nurse  of 
the  Cercaria. 

348.  The    Hydroid  Polyps   present   phenomena  no  less 
numerous  and  strange.     The  Campanularia  has  a  branching, 
plant-like  form,  with  little  cup-shaped  cells  on  the  ends  and  in 
the  axils  of  the  branches,  each  of  which  contains  a  little 
animal.     These  cups  have  not  all  the  same 
organization.     Those  at  the  extremity  of 

the  branches,  (a,)  and  which  appear  first, 
are  furnished  with  long  tentacles,  where- 
with they  seize  their  food,  (Fig.  143.) 
Those  in  the  axils  of  the  branches,  and 
which  appear  late,  are  females,  (£,)  and 
have  no  such  tentacles.  Inside  of  the  lat- 
ter, little  spherical  bodies  are  found,  each 
having  several  spots  in  the  middle ;  these 
are  the  eggs.  Finally,  there  is  a  third 
form,  different  from  the  two  preceding, 
produced  by  budding  from  the  female  polyp,  to  which  it  in 
some  sort  belongs,  (c.)  It  is  within  this  that  the  eggs  ar- 
rive, after  having  remained  some  time  within  the  female. 
Their  office  seems  to  be  to  complete  the  incubation,  for  it  is 
always  within  them  that  the  eggs  are  hatched. 

349.  Tr.3  little  animal,  on  becoming  free,  has  not   the 


166  REPRODUCTION. 

slightest  resemolaiue  .o  the  adult  polyp.     As  in  the  yc  jng 
Medusa,   the    body   is   cylindrical,   covered    with 
delicate   cilia.      After  having  remained    free    for 
some  time,  the  young  animal  fixes  itself  and  as- 
sumes a  flattened  form.     By  degrees,  a  little  swell- 
ing rises  from  the  centre,  which  elongates,  and  at 
last  forms  a  stalk.     This  stalk  ramifies,  and  we 
Fig.  144.     soon  recognize  in  it   the   animal   of   figure    143, 
with    the    three   kinds   of  buds,    which  we    may 
consider  as  three  distinct  forms  of  the  same  animal. 

350.  The  development  of  Campanularia  presents,  in 
some  respects,  an  analogy  to  what  takes  place  in  the  re- 
p reduction  of  plants,  and  especially  of  trees.  They  should 
be  considered  as  groups  of  individuals,  and  not  as  single 
individuals.  The  seed,  which  corresponds  to  the  embryo 
of  the  Hydroid,  puts  forth  a  little  stalk.  This  stalk  soon 
ramifies  by  gemmiparous  reproduction,  that  is,  by  throwing 
out  buds  which  become  branches.  But  ovulation,  or  repro- 
duction by  means  of  seeds,  does  not  take  place  until  an  ad- 
vanced period,  and  requires  that  the  tree  should  have  attained 
a  considerable  growth.  It  then  produces  flowers  with  pistils 
and  stamens,  that  is,  males  and  females,  which  are  com- 
monly united  in  one  flower,  but  which  in  some  instances  are 
separated,  as  in  the  hickories,  the  elders,  the  willows,  &c.* 

*  Several  plants  are  endowed  with  organs  similar  to  the  third  form  of 
buds,  as  seen  in  the  Campanularia ;  for  example,  the  liverwort,  (Marchan- 
tia  polymorpha,)  which  has  at  the  base  of  the  cup  a  little  receptacle,  from 
the  bottom  of  which  little  disk-like  bodies  are  constantly  forming,  which, 
when  detached,  send  out  roots,  and  gradually  become  complete  individu- 
als. Besides  that,  we  find  in  these  animals,  as  in  plants,  the  important 
peculiarity,  that  all  the  individuals  are  united  in  a  common  trunk,  which 
is  attached  to  the  soil ;  and  that  all  are  intimately  dependent  on  each 
other,  as  long  as  they  remain  united.  And  if  we  compare,  in  this  point 
of  view,  the  various  species  in  which  alternate  reproduction  has  been 
observed,  we  find  that  the  progress  displayed  in  each  type  consists  pre- 
cisely in  the  ir  creasing  freedom  of  the  individual  in  its  various  forms.  At 


CONSEQtfLNCES    OF   ALTERNATE    GENERATION  167 

SECTION   III. 

OONSEQTENCES    OF    ALTERNATE    GENERATION. 

351.  These  various  examples  of  alternate  generation  ren- 
der it  evident,  that  this  phenomenon  ought  not  to  be  consid- 
ered as  an  anomaly  in  Nature  ;  but  as  the  special  plarrof  de- 
velopment, leading  those  animals  in  which  it  occurs  to  the 
highest  degree  of  perfection  of  which  they  are  susceptible. 
Moreover,  it  has  been  noticed  among  all  types  of  inverte- 
bratH  animals ;  while  among  the  Vertebrates  it  is  as  yet 
unknown.     It  would  seem  that  individual  life  in  the  lowei 
animals   is  not  defined   within  so  precise  limits    as  in  the 
higher  types ;  owing,  perhaps,  to  the  greater  uniformity  and 
independence  of  their  constituent  elements,  the  cells,  and 
that,  instead  of  passing   at  one  stride  as  it  were,  through  all 
the  phases  of  their  development,  in  order  to  accomplish  it, 
they  must  either  be  born  in  a  new  form,  as  in  the  case  of 
alternate  generation,  or  undergo  metamorphoses,  which  are 
a  sort  of  second  birth. 

352.  Many  analogies  may  be  discovered  between  alternate 
reproduction  and  metamorphosis.     They  are  parallel  lines 
that  lead  to  the  same  end,  namely,  the  development  of  the 
species.     Nor  is  it  rare  to  see  them  coexisting  in  the  same 

first,  we  have  all  the  generations  united  in  a  common  trunk,  as  in  the 
lower  Polyps  and  in  plants;  then  in  the  Medusae  and  in  some  of  the 
Hydroid  Polyps  the  third  generation  begins  to  disengage  itself.  Among 
some  of  the  intestinal  worms,  (the  Distoma,)  the  third  generation  is 
enclosed  within  its  nurse,  and  this,  in  its  turn,  is  contained  in  the  body 
of  the  grand-nurse,  while  the  complete  Distoma  lives  as  a  parasitic  worm 
in  the  body  of  other  animals,  or  even  swims  freely  about  in  the  larva 
state,  as  Cercaria.  Finally,  in  the  Plant-lice,  all  the  generations,  the 
nuises  as  well  as  the  perfect  animals,  are  separate  individuals. 


168  REPRODUCTION. 

animal.  Thus,  in  the  Cercaria,  we  have  seen  an  animal  pro 
duced  from  a  nurse  afterwards  transformed  into  a  Distoma, 
by  undergoing  a  regular  metamorphosis. 

353.  In  each  new  generation,  as  in  each  new  metamor- 
phosis, a  real  progress  is  made,  and  the  form  which  results 
is  more  perfect  than  its  predecessor.     The  nurse  that  pro- 
duces the  Cercaria  is  manifestly  an  inferior  state,  just  as  the 
chrysalis  is  inferior  to  the  butterfly. 

354.  But  there   is  this  essential   difference   between  the 
metamorphoses  of  the  caterpillar  and  alternate  reproduction, 
that,  in  the  former  case,  the  same  individual  passes  through 
all  the  phases  of  development ;  whereas,  in  the   latter,  the 
individual   disappears,  and   makes  way  for  another,  which 
carries  out  what  its  predecessors  had  begun.     It  would  give 
a  correct  idea  of  this  difference  to  suppose  that  the  tadpole, 
instead  of  being  itself  transformed  into  a  frog,  should  die, 
having  first  brought  forth  young  frogs;  or  that  the  chrysalis 
should,   in   the  same  way,   produce  young  butterflies.     In 
either  case,  the  young  would  still  belong  to  the  same  species, 
but  the  cycle  of  development,  instead  of  being  accomplished 
in  a  single  individual,  would   involve  two  or  more  acts  of 
generation. 

355.  It  follows,  therefore,  that  the  general  practice  of  de- 
riving the  character  of  a  species  from  the  sexual  forms  alone, 
namely,  the  male  and  the  female,  is  not  applicable  to  all 
classes  of  animals  ;  since  there  are   large   numbers  whose 
various  phases  are  represented  by  distinct  individuals,  en- 
dowed with  peculiarities  of  their  own.     Thus,  while  in  the 
stag  the  species  is  represented  by  two  individuals  only,  stag 
and   hind,  the  Medusa,  on  the   other  hand,  is   represented 
under  the  form  of  three  different  types  of  animals  ;  the  first 
is  free,  like  the  Infusoria,  the  second  is  fixed  on  a  stalk,  like 
a  polyp,  and  the  third  again  is  free,  consisting  in  its  turn 
of  male  and  female.     In  the  Distoma,  also,  there  are  four 


CONSEQUENCES    OF    ALTERNATE    GENERAnrN.  169 

separate  individuals,  the  grand-nurse,  the  nurse,  the  larva  or 
Cercaria,  and  the  Distoma,  in  which  the  sexes  are  not  sepa- 
rate. Among  the  Aphides,  the  number  is  much  greater 
still. 

356.  The  study  of  alternate  generation,  besides  making 
us  better  acquainted  with  the  organization  of  the  lower  ani- 
mals, greatly  simplifies  our  nomenclature.     Thus,  in  future, 
instead  of  enumerating  the  Distoma  and  the  Cercaria,  or  the 
Strobila,  *he  Ephyra,  and   the  Medusa,  as  distinct  animals, 
belonging  to  different  classes  and  families,  only  the  name 
first  given  to  one  of  these  forms  will  be  retained,  and  the 
rest  be  struck  from  the   pages  of  Zoology,  as  representing 
only  the  transitory  phases  of  the  same  species. 

357.  Alternate    generation    always   presupposes   several 
modes  of  reproduction,  of  which  the  primary  is  invariably 
by    ovulation.      Thus,  we    have  seen  that  the  Polyps,  the 
Medusa,  the  Salpa,  &c.,  produce  eggs,  which  are  generally- 
hatched  within  the  mother.     The  subsequent  generation,  on 
the  contrary,  is  produced  in  a  different  manner,  as  we  have 
shown  in  the  preceding  paragraphs  ;  as  among  the  Medusae, 
by  transverse  division ;   among  the  Polyps  and  Salpae,  by 
buds,  &c. 

358.  The  subsequent  generations  are,  moreover,  not  to  be 
regarded  in  the  same  light  as  those  which  first  spring  directly 
from  eggs.     In  fact,  they  are  rather  phases  of  development, 
than  generations  properly  so  called  ;  they  are  either  without 
sex,  or  females  whose  sex  is  imperfectly  developed.     The 
nurses  of  the  Distoma,  the  Medusa,  and  sthe  Campanularia, 
are   barren,  and   have  none  of  the  attributes  of  maternity, 
except  that  of  watching  over  the  development  of  the  species, 
being  themselves  incapable  of  producing  young. 

359.  Another  important  result  follows  from  the  above  ob- 
servations    namely,    that  the   differences   between   animals 
which  are   produced   by  alternate   generation  are  less,  the 

15 


170  REPROIUCTION. 

earlier  the  epoch  at  which  we  examine  them.  No  two  ani 
mals  can  be  more  unlike  than  an  adult  Medusa  (Fig.  31 
and  an  adult  Campanularia,  (Fig.  143;)  they  even  seem  to 
belong  to  different  classes  of  the  Animal  Kingdom,  the  for- 
mer being  considered  as  an  Acaleph,  the  latter  as  a  Polyp. 
On  the  other  hand,  if  we  compare  them  when  first  hatched 
from  the  egg,  they  appear  so  much  alike  that  it  is  with  the 
greatest  difficulty  they  can  be  distinguished.  They  are 
then  little  Infusoria,  without  any  very  distinct  shape,  and 
moving  with  the  greatest  freedom.  The  larvae  of  certain 
intestinal  worms,  though  they  belong  to  a  different  depart- 
ment, have  nearly  the  same  form,  at  one'period  of  their  life. 
Farther  still,  this  resemblance  extends  to  plants.  The 
spores  of  certain  sea-weeds  have  nearly  the  same  appear- 
ance as  the  young  Polyp,  or, the  young  Medusa;  and  what 
is  yet  more  remarkable,  they  are  also  furnished  with  cilia, 
and  move  about  in  a  similar  manner.  But  this  is  only  a 
transient  state.  Like  the  young  Campanularia  and  the  young 
Medusa,  the  spore  of  the  sea-weed  is  free  for  only  a  short 
time  ;  soon  it  becomes  fixed,  and  from  that  moment  the 
resemblance  ceases. 

360.  Are  we  to  conclude,  then,  from  this  resemblance  of 
the  different  types  of  animals  at  the  outset  of  life,  that  there 
is  no  real  difference  between  them  ;  or  that  the  two  King 
doms,  the  Animal  and  the  Vegetable,  actually  blend,  bo- 
cause  their  germs  are  similar?  On  the  contrary,  we  thinK 
nothing  is  better  calculated  to  strengthen  the  idea  of  the 
original  separation  of  the  various  groups,  as  distinct  and 
independent  types,  than  the  study  of  their  different  phases. 
In  fact,  a  difference  so  wide  as  that  between  the  adult 
Medusa  and  the  adult  Campanularia  must  have  existed  even 
in  the  young ;  only  it  does  not  show  itself  in  a  manner 
appreciable  by  our  senses  ;  the  character  by  which  they 
subsequently  differ  so  much  being  not  yet  developed  To 


CONSEQUENCES    OF    ALTERNATE    GENERATIC  N.  171 

deny  the  realty  of  natural  groups,  because  of  these  early 
resemblances,  would  be  to  take  the  semblance  for  the 
reality.  It  would  be  the  same  as  saying  that  the  frog  and 
the  fish  are  one,  because  at  one  stage  of  embryonic  life  it  is 
impossible,  with  the  means  at  our  command,  to  distinguish 
them. 

361.  The  account  we  have  above  given  of  the  develop- 
ment, the  metamorphoses,  and  the  alternate  reproduction  of 
the  lower  animals,  is  sufficient  to  undermine  the  old  theory 
of  Spontaneous  Generation,  which  was  proposed  to  account 
for  the  presence  of  worms  in  the  bodies  of  animals,  for  the 
sudden  appearance  of  myriads  of  animalcules  in  stagnant 
water,  and  under  other  circumstances  rendering  their  occur- 
rence   mysterious.      We   need   only  to   recollect   how  the 
Cercaria  insinuates  itself  into  the 

skin  and  the  viscera  of  mollusks, 
(339,  342,)  to  understand  how 
admission  may  be  gained  to  the 
most  inaccessible,  parts.  Such  be- 
ings occur  even  in  the  eye  of  many  Fig.  145.  Fig.  14b. 
animals,  especially  of  fishes  ;  they 

are  numerous  in  the  eye  of  the  common  fresh-water  perch 
of  Europe.  To  the  naked  eye  they  seem  like  little  white 
spots,  (Fig,  145;)  but  when  magnified,  they  have  the  form 
of  Fig.  146. 

362.  As   to  the   larger  intestinal  worms  found   in  other 
animals,  the  mystery  of  their  origin  has  been  entirely  solved 
by  recent  researches.     A  single  instance  will  illustrate  tlveir 
history.     At  certain  periods  of  the  year,  the  Sculpins  of  the 
Baltic  are  infested  by  a  particular  species  of  Taenia  or  tape- 
worm, from  which  they  are  free  at  other  seasons.    Mr.  Esch- 
richt  found  that,  at  certain  seasons,  the  worms  lose  a  great 
portion  of  the  long  chain  of  rings  of  which  they  are  com- 
posed.    On  a  careful  examination,  he  found  that  earh  ring 


172  REPRODUCTION. 

contained  several  hundred  eggs,  which,  on  heing  freed  from 
their  envelop,  float  in  the  water.  As  these  eggs  are  innu- 
merable, it  is  not  astonishing  that  the  Sculpins  should  occa- 
sionally swallow  some  of  them  with  their  prey.  The  eggs, 
being  thus  introduced  into  the  stomach  of  the  fish,  find  con- 
ditions favorable  to  their  development ;  and  thus  the  species 
is  propagated,  and  at  the  same  time  transmitted  from  one 
generation  of  the  fish  to  another.  The  eggs  which  are  not 
s-.vallowed  are  probably  lost. 

363.  All  animals  swallow,  in  the  same  manner,  with  their 
food,  and  in  the  water  they  drink,  numerous  eggs  of  such 
parasites,  any  one  of  which,  finding  in  the  intestine  of  the 
animal  favorable  conditions,  may  be  hatched.     It  is  probable 
that  each  animal  affords  the  proper  conditions  for  some  par- 
ticular species  of  worm  ;  and  thus  we  may  explain  how  it  is 
that  most  animals  have  parasites  peculiar  to  themselves. 

364.  As  respects  the  Infusoria,  we  also  know  that  most 
of  them,  the   Rotifera  especially,  lay  eggs.     These  eggs, 
which  are  extremely  minute,  (some  of  them  only  -rs^iny  °f 
an  inch  in  diameter,)  are  scattered   every  where  in  great 
profusion,  in  water,  in  the  air,  in   mist,  and  even  in  snow. 
Assiduous  observers  have  not  only  seen  the  eggs  laid,  but 
moreover,  have  followed  their  development,  and  have  seen 
the  young  animal  forming  in  the  egg,  then  escaping  from  it, 
increasing  in  size,  and,  in  its  turn,  laying  eggs.     They  have 
been  able,  in  some  instances,  to  follow  them  even  to  the  fifth 
and  sixth  generation. 

365.  This  being  the  case,  it  is   much   more  natural  to 
suppose  that  the  Infusoria  *  are  products  of  like  germs,  than 


*  In  this  connection,  it  ought  to  he  remembered  that  a  large  proportion 
of  the  so-called  Infusoria  are  not  independent  animals,  but  immature 
germs,  belonging  to  different  classes  of  the  Animal  Kingdom,  and  that 
many  must  be  refeired  to  the  Vegetable  Kingdom. 


SPONTANEOUS    GENERATION.  173 

.o  assign  to  them  a  spontaneous  origin  altogether  incompati- 
ole  with  what  we  know  of  organic  development.  Their 
rapid  appearance  is  not  at  all  astonishing,  when  we  reflect 
ihat  some  mushrooms  attain  a  considerable  size  in  a  few 
hours,  but  yet  pass  through  all  the  phases  of  regular  growth ; 
and,  indeed,  since  we  have  ascertained  the  different  modes  of 
generation  among  the  lower  animals,  no  substantial  difficul- 
ties to  the  ax'om  "  omne  vivum  sx  ovo"  (275,)  any  longer 

exist. 

15* 


CHAPTER     TWELFTH. 

METAMORP  IOSES    OF   ANIMALS. 

366.  UNDER  the  name  of  metamorphoses  are   included 
lliose  changes  which  the  body  of  an  animal  undergoes  after 
its  birth,  and  which  are  modifications,  in  various  degrees,  of 
»ts  organization,  form,  and  its  mode  of  life.     Such  changes 
are  not  peculiar  to  certain  classes,  as  has  been  so  long  sup- 
posed, but  are  common  to  all  animals,  without  exception. 

367.  Vegetables  also  undergo  metamorphoses,  but  with 
this  essential  difference,  that  in  vegetables  the  process  con- 
sists in  an  addition  of  new  parts  to  the  old  ones.    A  succession 
of  leaves,  differing  from  those  which  preceded  them,  comes 
on  each  season  ;  new  branches  and  roots  are  added  to  the 
old  stem,  and  woody  layers  to  the  trunk.     In  animals,  the 
whole  body  is  transformed,  in  such  a  manner  that  all  the 
existing  parts  contribute  to  the  formation  of  the  modified 
body.     The  chrysalis  becomes  a  butterfly ;  the  frog,  after 
having  been  herbivorous  during  its  tadpole  state,  becomes 
carnivorous,  and  its  stomach  is  adapted  to  this  new  mode  of 
life;  at  the  same  time,  instead  of  breathing  by  gills,  it  be- 
comes an  air-breathing  animal ;  its  tail  and  the  gills  disap- 
pear; lungs  and  legs  are  being  developed,  and,  finally,  it  is 
to  live  and  move  on  land. 

368  The  nature,  the  duration,  and  importance  of  meta- 
morphoses, as  also  the  epoch  at  which  they  take  place,  are 
infinitely  varied.  The  most  striking  changes  which  naturally 
present  themselves  to  the  mind  when  we  speak  of  metamoi 


METAMORPHOSES    OF    ANIMALS.  175 

phoses,  are  those  occurring  in  insects.  Not  merely  is  there 
a  change  of  physiognomy  and  form  observable,  or  an  organ 
more  or  less  formed,  but  their  whole  organization  is  modified. 
The  animal  enters  into  new  relations  with  the  external  world, 
while,  at  the  same  time,  new  instincts  are  imparted  to  it.  It 
has  lived  in  water,  and  respired  by  gills ;  it  is  now  furnished 
with  air-tubes,  and  breathes  in  the  atmosphere.  It  passes  by, 
with  indifference,  objects  which  before  were  attractive,  and 
its  new  instincts  prompt  it  to  seek  conditions  which  would 
have  been  most  pernicious  during  its  former  period  of  life. 
All  these  changes  are  brought  about  without  destroying  the 
individuality  of  the  animal.  The  mosquito,  which  to-day 
haunts  us  with  its  shrill  trumpet,  and  pierces  us  for  our 
blood,  is  the  same  animal  that,  a  few  days  ago,  lived  obscure 
and  unregarded  in  stagnant  water,  under  the  guise  of  a  little 
worm. 

369.  Every  one  is  familiar  with  the  metamorphoses  of  the 
silk-worm.  On  escaping  from  the  egg,  the  little  worm  or 
caterpillar  grows  with  great  rapidity  for  twenty  days,  when 
!t  ceases  to  feed,  spins  its  silken  cocoon,  casts  its  skin,  and 
remains  enclosed  in  its  chrysalis  state.*  During  this  period 
of  its  existence,  most  extraordinary  changes  take  place.  The 
jaws  with  which  it  masticated  mulberry  leaves  are  trans- 
formed into  a  coiled  tongue  ;  the  spinning  organs  are  reduced  t 
the  gullet  is  lengthened  and  more  slender;  the  stomach, 
which  was  nearly  as  long  as  the  body,  is  now  contracted  into 
a  short  bag ;  the  intestine,  on  the  contrary  becomes  elon- 
gated and  narrow.  The  dorsal  vessel  is  shortened.  The 
ganglions  of  the  thoracic  region  approach  each  other,  and 
unite  into  a  single  mass.  Antennas  and  palpi  are  developed  on 
the  head,  and  instead  of  simple  eyes  appear  compound  ones. 


*  In  the  raising  of  silk-worms  this  period  is  not  waited  for,  but  «he  ani 
mal  is  killed  as  soon  as  it  has  spun  its  cocoon. 


176  METAMORPHOSES    OF   AN1MAL3. 

The  muscles,  which  before  were  uniformly  distributed,  (159,) 
are  now  gathered  into  masses.  The  limbs  are  elongated, 
and  wings  spring  forth  from  the  thorax.  More  active  motions 
then  reappear  in  the  digestive  organs,  and  the  animal,  burst- 
ing the  envelop  of  its  chrysalis,  issues  in  the  form  of  a  winged 
moth. 

370  The  different  external  forms  which  an  insect  may 
assume  is  well  illustrated  by  one  which  is  unfortunately  too 
well  known  in  this  country,  namely,  the  canker-worm.  Its 
eggs  are  laid  on  posts  and  fences,  or  upon  the  branches  of  our 
apple-trees,  elms,  and  other  trees.  They  are  hatched  about 
the  time  the  tender  leaves  of  these  trees  begin  to  unfold. 
0-6  o  d 


r 


Fig.  147. 

The  caterpillar  (a)  feeds  on  the  leaves,  and  attains  its  full 
growth  at  the  end  of  about  four  weeks,  being  then  not  quite 
an  inch  in  length.  It  then  descends  to  the  ground,  and  en- 
ters the  earth  to  the  depth  of  four  or  five  inches,  and  having 
excavated  a  sort  of  cell,  is  soon  changed  into  a  chrysalis  or 
nymph,  (b.)  At  the  usual  time  in  the  spring,  it  bursts  the 
SKin,  and  appears  in  its  perfect  state,  under  the  form  of  a 
moth,  (d.)  In  this  species,  however,  only  the  male  has 
wings.  The  perfect  insects  soon  pair,  the  female  (c)  crawls 
up  a  tree,  and,  having  deposited  her  eggs,  dies. 

371.  Tiansformations  no  less  remarkable  are  observed 
among  the  Crustacea.  The  metamorphoses  in  the  family  of 
Cirrhipedes  are  especially  striking.  It  is  now  known  that 
the  barnacles,  vBalanus,)  which  have  been  arranged  among 
the  mollusks,  are  truly  crustaceans ;  and  this  result  of  modern 
researches  has  been  deduced  in  the  clearest  manner  from  the 


METAMORPHOSES    OF    ANIMALS. 


m 


study  of  their  transformations.     The  following  figures  repre- 
sent the  different  phases  of  the  duck-barnacle,  (Anatifa.) 

a  b  e 


Fig.  148. 


372.  The  Anatifa,  like  all  Crustacea,  is  reproduced  by 
eggs,  specimens  of  which,  magnified  ninety  diameters,  are 
represented  in  figure  148,  a.     From   these   eggs  little  ani- 
mals issue,  which  have  not  the  slightest  resemblance  to  the 
parent.     They  have  an  elongated  form,  (ft,)  a  pair  of  ten- 
acles,  and  four  legs,  with  which  they  swim  freely  in  the 
water. 

373.  Their  freedom,  however,  is  of  but  short  duration. 
The  little  animal  soon  attaches  itself  by  means  of  its  tenta- 
cles, having  previously  become  covered  with  a  transparent 
shell,  through  which  the  outlines  of  the  body,  and  also  a  very 
distinct  eye,  are  easily  distinguished,  (Fig.  148,  c.)     Figure 
148,  d,  shows  the  animal  taken  out  of  its  shell.     It  is  plainly 
seen  that  the  anterior  portion  has  become  considerably  en- 
larged.    Subsequently,  the    shell   becomes  completed,  and 
the  animal  casts  its  skin,  losing  with  it  both  its  eyes  and  its 
tentacles.     On  the  other  hand,  a  thick  membrane  lines  the 
interior  of  the  shell,  which   pushes  out  and  forms  a  stem, 
(e,)  by  means  of  which  the  animal  fixes  itself  to  immersed 
bodies,  after  the  loss  of  its  tentacles.     This  stem  gradually 
enlarges,  ana  the  animal  soon  acquires  a  definite  shape,  such 


178  METAMORPHOSES    OF    ANIMALS. 

as  it  is  rep  escnted  in  figure  148,  /,  attached  to  a  piece  of 
floating  wood 

374.  There  is,  consequently,  not  only  a  change  of  organi- 
zation in  the  course  of  the  metamorphoses,  but  also  a  change 
of  faculties  and   mode  of  life.     The  animal,  at  first  free, 
becomes   fixed ;    and    its    adhesion    is   effected    by    totally 
different  organs  at  different  periods  of  life,  first  by  means  of 
centacles,   which  were    temporary   organs,   and   afterwards 
by  means  of  a  fleshy  stem  developed  especial.y  for  that 
purpose. 

375.  The  Radiata  also  furnish  us  with  examples  of  vari- 
ous metamorphoses,   especially  among  the    star-fishes.     A 
small  species  living  on  the  coast  of  New  England  (EcM~ 
naster    sanguinolentus)    undergoes    the    following    phases, 
(Fig.  149.) 


Fig.  149. 

376.  If  the  eggs  are  examined  by  the  microscope,  each 
one  is  found  to  contain  a  small,  pear-shaped  body,  which 
is  the  embryo,  (e,)  surrounded  by  a  transparent  envelop. 
On  escaping  from  the  egg,  the  little  animal  has  an  oblong 
form,  with  a  constriction  at  the  base.  This  constriction 
becoming  deeper  and  deeper  forms  a  pedicle,  (p,)  which 
soon  divides  into  three  lobes.  The  disk  also  assumes  a  pen- 
tagonal form,  with  five  double  series  of  vesicles.  The  first 
rudiments  of  the  rays  are  seen  to  form  in  the  interior  of  the 
pentagon.  At  the  same  time,  the  peduncle  contracts  still 
more,  being  at  last  entirely  absorbed  into  the  cavity  of  the 
body,  and  the  animal  soon  acquires  its  final  form,  (m.) 


METAMORPHOSES    OF    ANIMALS. 


179 


Fig.  151. 


377.  Analogous  transformations  take  place  in  the  Cc  nat- 

ula.  In  early  life 
(Fig.  150)  it  is 
fixed  to  the  ground 
by  a  stem,  but  be- 
comes detached  at 
a  certain  epoch, 
and  then  floats 
freely  in  the  sea, 
(Fig.  151.)  On 
the  other  hand, 

the     Polypi     seem    to    follow    a    icverso 
course,  many  of  them  becoming  fixed    to 
the   ground  after    having   been    previously 
Fig.  150.         free. 

378.  The    metamorphoses    of    mollusks,    though    less 
striking,  are  not  less   worthy  of  notice.     Thus,  the  oyster, 
with  which    we  are  familiar  in  its  adhering  shell,  is  free 
when  young,  like  the  clam  (Mya)  and  most  other   shell- 
fishes.    Others,  which  are  at  first  attached  or  suspended  to 
the  gills  of  the  mother,  afterwards  become  free,  as  the  Unio. 
Some  naked  Gasteropods,  the  Acteon  or  the  Eolis,  for  ex- 
ample,  are  born  with  a  shell,  which  they  part  with  shortly 
after  leaving  the  egg. 

379.  The  study  of  metamorphoses  is,  therefore,  of  the 
utmost  importance  for  understanding  the  real   affinities  of 
animals  very  different  in  appearance,  as  is  readily  shown  by 
(he  following  instances.     The  butterfly  and  the  earth-worm 
seem,  at  the    first  glance,  to   have   no   relation    whatever. 
They  Differ  in  their  organization,  no  less  than  in  their  out 
ward  appearance.     But,  on  comparing  the  caterpillar  and 
the  worm,  these  two  animals  closely  resemble  each- other. 
The   analogy,   however,   is   only   transient;    it   lasts    only 
during  the  larva  state  of  the  caterpillar,  and  is  effaced  as  it 


180  METAMORPHOSES  OF  ANIMALS. 

passes  to  the  chrysalis  and  butterfly  states.  The  latter  be 
comes  a  more  and  more  perfect  animal,  whilst  the  worm 
remains  in  its  inferior  state. 

380.  Similar  instances  are  furnished  by  animals  belong 
ing  to  all  the  types  of  the  Animal  Kingdom.     Who  would 
think,  at  first  glance,  that  a   Barnacle  or  an  Anatifa  were 
more  nearly  allied  to  the  crab  than   to  the  oyster?     And, 
nevertheless,  we  have  seen,  (372,)  in  tracing  back  the  Anat- 
ifa to  its  early  stages,  that  it  then  bears  a  near  resemblance 
to  a  little  Crustacean,  (Fig.  148,  d.)     It  is  only  when  full 
grown-  that  it  assumes  its  peculiar  mollusk-Iike  covering. 

381.  Among   the   Cuttle-fishes    there    are    several,   the 
Loligo,  (Fig.  47,)  for  example,  which  are  characterized  by 
the  form    of  their   tentacles,  the   two    interior   being    much 
longer  than  the  others,  and  of  a   different  form  ;  whilst  in 
others,  as  the  Octopus,  they  are  all  equal.     But  if  we  com- 
pare the  young,  we  find  that  in   both  animals  the  tentacles 
are  all  equal,  though  they  differ  in  number.     The  inequality 
in  the  tentacles  is  the  result  of  a  further  development.-- 

382.  Among  the  Radiata,  the  Pentacrinus  and  the  Comat- 
ula  exemplify  the  same  point.     The  two  are  very  different 
when  full  grown,  the  latter  being  a  free-swimming  star-fish, 
(Fig.  151,)  while  the  former  is  attached  to  the  soil,  like  a 
Polyp.     But  we  have  seen  (377)  that  the  same  is  the  case 
with  Comatula  in  its  early  period ;  and  that,  in  consequence 
of  a  further  metamorphosis,  it  becomes  disengaged  from  its 
stem,  a/id  floats  freely  in  the  water. 

383.  In  the  type  of  Vertebrates,  the  considerations  drawn 
from  metamorphoses  acquire  still  greater  importance  in  ref- 
erence to  classification.     The  Sturgeon  and  the  White-fish, 
before  mentioned,  (306,)  are  two  very  different  fishes  ;  yet, 
taking  into  consideration  their   external  form  and   bearing 
merely,   it   might  be  questioned  which  of  the    two    should 
take  the    highest  rank  ;    whereas  the  doubt    is    very  easily 


METAMORPHOSES   OP   ANIMALS.  181 

resolved  by  an  examination  of  their  anatomical  structure. 
The  White-fish  has  a  skeleton,  and,  moreover,  a  vertebral 
column,  composed  of  firm  bone.  The  Sturgeon,  (Fig.152), 


Fig.  152. 

on  the  contrary,  has  no  bone  in  the  vertebral  column,  except 
the  spines  or  apophyses  of  the  vertebra?.  The  middle  part, 
or  body  of  the  vertebra,  is  cartilaginous  ;  the  mouth  is  trans- 
verse,  and  underneath  the  head  ;  and  the  caudal  fin  is  un- 
equally forked,  while  in  the  White-fish  it  is  equally  forked. 

384.  If,  however,  we  observe  the  young  White-fish  jusl 
after  it  has  issued  from  the  egg,  (Fig.  123,)  the  contrast  will 
be  less  striking.     At  this  period  the   vertebrae  are  cartilagi- 
nous, like  those  of  the  Sturgeon  ;  its  mouth,  also,  is  trans- 
verse and  inferior,  and  its  tail  undivided  ;  at  that  period  the 
White-fish  and  the  Sturgeon  are,  therefore,  much  more  alike. 
But  this  similarity  is  only  transient ;  as  the  White-fish  grows, 
its  vertebras  become  ossified,  and   its  resemblance    to  the 
Sturgeon  is  comparatively  slight.     As  the  Sturgeon  has  no 
such  transformation  of  the  vertebras,  and  is,  in  some  sense, 
arrested  in  its  development,  while  the  White-fish  undergoes 
subsequent  transformation,  we  conclude  that,  compared  with 
the  White-fish,  it  is  really  inferior  in  rank. 

385.  This  relative  inferiority  and  superiority  strikes   us 
still  more  when  we  compare  with  our  most   perfect  fishes 
(the  Salmon,  the  Cod)  some  of  those  worm-like  animals,  so 
different  from  ordinary  fishes  that  they  were  formerly  placed 
among  the  worms.     The  Am- 

phioxus,  represented  of  its  nat- 
ural size,  (Fig.  153,)  not  only 
16 


182  METAMORPHOSES    OF    ANIMALS. 

has  no  bony  skeleton,  but  not  even  a  head,  properly  spoak 
ing.  Yet.  the  fact  that  it  possesses  a  dorsal  cord,  extending 
from  one  extremity  of  the  body  to  the  other,  proves  that  it 
belongs  to  the  type  of  Vertebrates.  But  as  this  peculiar 
structure  is  found  only  at  a  very  early  period  of  embiyonic 
development,  in  other  fishes,  we  conclude  that  :he  Amphi- 
oxus  holds  the  very  lowest  rank  in  this  class. 

386.  Nevertheless,  the  metamorphoses  of  animals  after 
birth,  will,  in  many  instances,  present  but  trifling  modifica- 
tions of  the  relative  rank  of  animals,  compared  with  those 
which  may  be  derived  from  the  study  of  changes  picvious 
to  that  period,  as  there  are  many  animals  which  undergo  no 
changes  of  great  importance  after  their  escape  from  the  egg, 
and   occupy,  nevertheless,  a   high   rank   in   the   Zoological 
series,  as,  for  example,  Birds  and  Mammals.     The  question 
is,  whether  such  animals  are  developed  according  to  differ- 
ent plans,  or  whether  their   peculiarity  in   that   respect    is 
merely  apparent.     To  answer  this  question,  let  us  go  back 
to  the  period  anterior  to  birth,  and  see  if  some  parallel  may 
not  be  made  out  between  the   embryonic  changes  of  these 
animals   and  the   metamorphoses  which  take  place  subse- 
quently to  birth  in  others. 

387.  We  have   already  shown  that  embryonic   develop- 
ment consists  in  a  series  of  transformations ;  the  young  ani- 
mal enclosed  in  the  egg  differing  at  each  period  of  its  de- 
velopment, from  what  it. was    before.     But   because   these 
transformations  precede  birth,  and  are,  there  fore,  not  generally 
observed,  they  are  not  less  important.     To  be  satisfied  that 
these  transformations  are  in   every  respect  similar  to  those 
which  follow  birth,  we  have  only  to  compare  the  changes 
which  immediately  precede  birth  with  those  which  immediate- 
ly follow  it,  and  we  shall  readily  perceire  that  the  latter  arc 
simply  a  continuation  of  the  former,  till  all  are  completed. 

388.  Let  rs  recur  to  the  development  of  fishes  for   llus 


METAMORPHOSES    OF    A.IIMALS.  183 

trntion.  The  young  White-fish,  as  we  have  seen,  (315,)  is 
far  from  having  acquired  its  complete  development  when 
born.  The  vertical  fins  are  not  yet  separate  ,  the  mouth  has 
not  yet  its  proper  position  ;  the  yolk  has  not  yet  retreated 
within  the  cavity  of  the  body,  but  hangs  below  the  chest  in 
the  form  of  a  large  bag.  Much,  therefore,  remains  to  be 
changed  before  its  development  is  complete.  But  the  fact 
that  it  has  been  born  does  not  prevent  its  future  evolution, 
which  goes  on  without  interruption. 

389.  Similar  inferences  may  be  drawn  from  the  develop- 
ment of  the  chicken.     The  only  difference  is,  that  the  young 
chicken  is  born  in  a  more  mature  state,  the  most  important 
transformations  having  taken  place  during  the    embryonic 
period,  while  those  to  be  undergone  after  birth  are  less  con- 
siderable, though  they  complete  the   process  begun  in  the 
embryo.      Thus  we  see    it,  shortly  after  birth,  completely 
changing  its  covering,  and   clothed  with  feathers  instead  of 
down ;  still  later  its  crest  appears,  and  its  spurs  begin  to  be 
developed. 

390.  In   certain    Mammals,  known    under  the  name  of 
Marsupials,  (the  Opossum  and  Kangaroo,)  the  link  between 
the  transformations  which  take  place  before  birth,  and  those 
that  occur  at  a  later  period,  is  especially  remarkable,    These 
animals  are  brought  into  the  'world  so  weaK  and  undeveloped 
that  they  have  to  undergo  a  second  gestation,  in  a  pouch  with 
which  the  mother  is  furnished,  and  in  which  the  young  remain, 
each  one  fixed   to  a  teat,  until  they  are  entirely  developed. 
Even  those  animals  which  are  born  nearest  to  the  complete 
state,    undergo,     nevertheless,    embryonic     transformations. 
Ruminants  acquire  their  horns;  and  the  lion  his  mane.    Mosi 
mammals,  at  birth,  are  destitute  of  teeth,  and   incapable  of 
using  their  limbs ;  and  all  are  dependent  on  the  mother  and 
the  milk  secreted  by  her,  until  the  stomach  is  capable  of 
digesting  other  aliments. 


184  METAMORPHOSES     OF    ANIMALS. 

391.  If  it  be  thus  shown  that  the  transformations 
which  take  place  in  the  embryo  are  of  the  same  nature, 
and  of  the  same  importance,  as  those  which  occur  after- 
wards, the  circumstance  that  some  precede  and  others 
succeed  birth  cannot  mark  any  radical  distinction  be- 
tween them.     Both  are  processes  of  the  life  of  the  indi- 
vidual.    Now,  as  life  does  not  commence  at  birth,  but 
goes  still  farther  back,  it  is  quite  clear  that  the  modifi- 
cations which  supervene  during  the  former  period  are 
essentially  the  same  as,  and  continuous  with,  the  latei 
ones ;   and  hence,  that  metamorphoses,  far  from  being 
exceptional  i#  the  case  of  Insects,  are  one  of  the  gen- 
eral features  of  the  Animal  Kingdom. 

392.  We  are,  therefore,  perfectly  entitled  to  say  that 
all  animals,  without  exception,  undergo  metamorphoses. 
Were  it  not  so,  we  should  be  at  a  loss  to  conceive  why 
animals  of  the  same  division  present  such  wide  differ- 
ences ;  and  that  there  should  be,  as  in  the  class  of  Rep- 
tiles,  some  families  that  undergo  important  metamor- 
phoses, (the  frogs,  for  example,)  and  others  in  which 
nothing  of  the  kind  is  observed  after  birth,  (the  Lizards 
and  Tortoises.) 

393.  It  is  only  by  connecting  the  two  kinds  of  trans- 
formations, namely,  those  which  take  place  before,  and 
those  after  birth,  that  we  -are  furnished  with  the  means 
of  ascertaining  the  relative  perfection  of  an  animal ;  in 
other  words,  these  transformations  become,  under  such 
circumstances,  a  natural  key  to  the  gradation  of  types. 
At  the  same  time,  they  will  force  upon  us  tne  convic- 
tion that  there  is  an  immutable  principle  presiding  over 
all  these  changes,  and  regulating  them  in  a  peculiar 
manner  in  each  animal. 

394.  These  considerations   are   exceedingly  impor- 
tant, not  only  from  their  bearing  upon  classification, 
but  not  less   so   from  the  application  which  may  be 
made  of  them  to  the  study  of  fossils.     If  we  exam- 
ine  attentively  the    fishes    that  have  been   found   in 
the  different   strata    of    the    earth,    we    remark  that 


METAMORPHOSES    OF    ANIMALS.  185 

those  of  the  most  ancient  deposits  have,  in  general,  preserved 
only  the  apophyses  of  their  vertebra?,  whilst  the  vertebrae 
then  selves  are  wanting.  Were  the  Sturgeons  of  the  Amer- 
ican rivers  to  become  petrified,  they  would  be  found  in  a 
similar  state  of  preservation.  As  the  apophyses  are  the 
only  bony  portions  of  the  vertebral  column,  they  alone 
would  be  preserved.  Indeed,  fossil  Sturgeons  are  known, 
which  are  in  precisely  this  condition. 

395.  From  the  fact  above  stated,  we  may  conclude  that 
the  oldest  fossil  fishes  did  not  pass  through  all  the  metamor- 
phoses which  our  osseous  fishes  undergo  ;  and,  consequently, 
that  they  were  inferior  to  analogous  species  of  the  present 
epoch  which  have  bony  vertebrae.  Similar  considerations 
apply  to  the  fossil  Crustacea  and  to  the  fossil  Echinoderms, 
when  compared  with  living  ones,  and  will,  probably,  be 
true  of  all  classes  of  the  Animal  Kingdom,  when  fully  studied 
as  to  thsir  geological  succession. 
16* 


*" 

CLAPTER    THIRTEENTH. 

GEOGRAPHICAL    DISTRIBUTION    OF    ANIMALS 
SECTION    I. 

GENERAL    LAWS    OF    DISTRIBUTION. 

396  No  animal,  excepting  man,  inhabits  every  part  of  the 
surface  of  the  earth.  Each  great  geographical  or  climatal 
region  is  occupied  by  some  species  not  found  elsewhere ; 
and  each  animal  dwells  within  certain  limits,  beyond  which 
it  does  not  range  while  left  to  its  natural  freedom,  and  within 
which  it  always  inclines  to  return,  when  removed  by  acci- 
dent or  design.  Man  alone  is  a  cosmopolite.  His  domain  is 
the  whole  earth.  For  him,  and  with  a  view  to  him,  it  was 
created.  His  right  to  it  is  based  upon  his  organization  and 
his  relation  to  Nature,  and  is  maintained  by  his  intelligence 
and  the  perfectibility  of  his  social  condition. 

397.  A  group  of  animals  which  inhabits  any  particular 
region,  embracing  all  the  species,  both  aquatic  and  terrestrial, 
is  called  its  FAUNA  ;  in  the  same  manner  as  the  plants  of  a 
country  are  called  its  Flora.  To  be  entitled  to  this  name,  it 
is  not  necessary  that  none  of  the  animals  composing  the 
group  should  be  found  in  any  other  region ;  it  is  sufficient 
that  there  should  be  peculiarities  in  the  distribution  of  the 
families,  genera,  and  species,  and  in  the  preponderance  of 
certain  types  over  others,  sufficiently  prominent  to  impress 
upon  a  region  well-marked  features.  Thus,  for  example,  in 
the  islands  of  the.  Pacific  are  found  terrestrial  animals,  alto 


GENERAL    LAWS    OF    DISTRIBUTION.  187 

getlier  peculiar,  and  not  found  on  the  nearest  cont.nents. 
There  are  numerous  animals  ,n  New  Holland  differing  from 
any  found  on  the  continent  of  Asia,  or,  indeed,  on  any  other 
part  of  the  earth.  If,  however,  some  species  inhabiting  both 
shores  of  a  sea  which  separates  two  terrestrial  regions  are 
found  to  be  alike,  we  are  not  to  ocnclude  that  those  regions 
have  the  same  Fauna,  any  more  than  that  the  Flora  of  Lap- 
land and  England  are  alike,  because  some  of  the  sea-weeds 
found  on  both  their  shores  are  the  same. 

398.  There  is  an  evident  relation  between  the  fauna  of 
any  locality  and  its  temperature,  although,  as  we  shall  here- 
after see,  similar  climates  are  not  always  inhabited  by  similffi 
animals,  (401,  402.)     Hence  the  faunas  of  the  two  hemis- 
pheres have  been  distributed  into  three  principal  divisions, 
namely,  the  arctic,  the  temperate,  and  the  tropical  faunas ; 
in  the  same  manner  as  we  have  arctic,  temperate,  and  tropi- 
cal floras.     Hence,  also,  animals  dwelling  at  high  elevations 
upon  mountains,  where  the  temperature  is  much  reduced 
resemblWhe  animals  of  colder  latitudes,  rather  than  those  of 
the  surrounding  plains. 

399.  In  some  -respects,  the  peculiarities  of  the  fauna  of  a 
region  depend  upon  its  flora,  at  least  so  far  as  land  animals 
are   concerned ;    for   herbivorous   animals   will   exist   only 
where  there  Is  an  adequate  supply  of  vegetable  food.     But 
taking  the  terrestrial  and  aquatic  animals  together,  the  limi- 
tation of  a  fauna  is  less  intimately  dependent  on  climate 
than  that  of  a  flpra.     Plants,  in  truth,  are  for  the  most  part 
terrestrial,  (marine  plants  being  relatively  very  few,)  wh:le 
animals  are  chiefly  aquatic.     The  ocean  is  the  true  home  of 
the  Animal  Kingdom ;    and  while  plants,  with  the   excep 
tion  of  the  lichens  and  mosses,  become  dwarfed,  or  perish 
under   the   influence    of  severe   cold,  the   sea   teems  with 
animals  of  all  classes,  far  beyond  the  extreme  limit  of  flower- 
ing plants, 


188  GEOGRAPHICAL    DISTRIBUTION    OF    ANIMALS. 

400.  The  influence  of  climate,  in  the  colder  regions,  acvs 
merely  to   induce  a  greater  uniformity   in   the  species  of 
animals.     Thus  the  same  animals  inhabit  the  northern  polar 
regions  of  the  three  continents.     The.  polar  bear  is  the  same 
in  Europe,  Asia,  and  America,  and  so  are  also  a  great  many 
birds.      In    t.ie    temperatg   regions,   on   the   contrary,    the 
species  differ  on  each  of  the  continents,  but  they  still  pre 
serve  the  same  general  features.     The  types  are  the  same 
but   they  are   represented    by   quite   different    species.      In 
consequence  of  these  general  resemblances,  the  first  colo- 
nists  of  New  England  erroneously  applied  the   names   of 
European  species  to  American  animals.     Similar  differences 
are  observed  in  distant  regions  of  the  same  continent,  within 
the  same  parallels  of  latitude.     The  animals  of  Oregon  and 
of  California  are  not  the  same  as  those  of  New  England. 
The   difference,  in  certain  respects,   is  even   greater  than 
between  the  animals  of  New  England  and  Europe.     In  like 
manner,  the  animals  of  temperate  Asia  differ  more  from  those 
of  Europe  than  they  do  from  those  of  America. 

401.  Under  the  torrid  zone,  the  Animal  Kingdom,  as  well 
as  the  Vegetable,  attains  its  highest  development.     The  ani- 
mals of  the  tropics  are  not  only  different  from  those  of  the 
temperate    zone,  but,   moreover,   they  present  the  greatest 
variety  among  themselves.     The   most   gracefully   propor- 
tioned forms  are  found  by  the  side  of  the  most  grotesque, 
decked  with  every  combination  of  brilliant  coloring.     At  the 
same  time,  the  contrast  between  the  animals  pf  different  con- 
tinents is  more  marked ;  and,  in  many  respects,  the  animals 
of  the  different  tropical  faunas  differ  not  less  from  each  other 
than  from  those  of  the  temperate  or  frozen  zones.     Thus, 
the   fauna  of  Brazil  varies  as  much  from    that  of  Central 
Africa  as  from  that  of  the  United  States. 

402.  This  diversity  upon  different  continents  cannot  de- 
pend simply  on  any  influence  of  the  climate  of  the  tropics 


GENERAL    LAWS    OF    «ISTRIBUTION.  189 

if  it  were  so  uniformity  ought  to  be  restored  in  proportion 
as  we  recedi  from  the  tropics  towards  the  antarctic  tern 
perate  regions.  But,  instead  of  this,  the  differences  con- 
tinue to  increase  ;  —  so  much  so,  that  no  faunas  are  more  in 
contrast  than  those  of  Cape  Horn,  the  Cape  of  Good  Hope, 
and  New  Holland.  Hence,  other  influences  must  be  in  oper- 
ation besides  those  of  climate;  —  influences  of  a  highei 
order,  which  are  involved  in  a  general  plan,  and  intimately 
associated  with  the  development  of  life  on  the  surface  of  the 
earth. 

403.  Faunas  are  more  or  less  distinctly  limited,  according 
to  the  natural  features  of  the  earth's  surface.     Sometimes 
two  faunas  are  separated  by  an  extensive  chain  of  moun 
tains,  like  the  Rocky  Mountains.     Again,  a  desert  may  in- 
tervene, like  the  desert  of  Sahara,  which  separates  the  fauna 
of  Central  Africa  from  that  of  the  Atlas  and  the   Moorish 
coast,  the  latter  being  merely  an  appendage  to  the  fauna 
of  Europe.     But  the  sea  effects  the  most  complete  limita- 
tion.    The  depths  of  the  ocean  are  quite  as  impassable  for 
marine  species  as  high  mountains  are  for  terrestrial  animals. 
It  would    be  quite   as  difficult  for  a  fish   or  a  mollusk  to 
cross  from  the  coast  of  Europe  to  the  coast  of  America,  as 
it  would  be  for  a   reindeer  to  pass  frcm  the  arctic  to  the 
antarctic  regions,  across  the  torrid  zone.     Experiments  of 
dredging  in  very  deep  water  have  also  taught  us  that  the 
abyss  of  the  ocean -is   nearly  a  desert.     Not  only  are  no 
materials  found  there  for  sustenance,  but  it  is  doubtful  if  ani- 
mals could  sustain  the  pressure  of  so  great   a  column  of 
water,  although  many  of  them  are  provided  with  a  system  of 
pores,  (260,)  which  enables  them  to  sustain  a  much  g-eater 
pressure  than  terrestrial  animals. 

404.  When  there  is  no  great  natural  limit,  the  transition 
from  one  fa  ana  to  another  is  made   insensibly.     Thus,  in 
passing  fronn    he  arctic  to  the  temperate  regions  of  North 


190  GEOGRAPHICAL    DISTR1BUT  ON    OF    ANIMALS 

America,  one  species  takes  th3  place  of  anott  er,  a  third  suc- 
ceeds the  second,  and  so  on,  until  finally  the  fauna  is  found 
to  be  completely  changed,  though  it  is  not  always  possible 
to  mark  the  precise  line  which  divides  the  one  from  the 
other. 

405.  The  range  of  species  does  not  at  all  depend  upon 
their  powers  of  locomotion  ;  if  it  were  so,  animals  which 
move  slowly  and  with  difficulty  would  have  a  narrow  range, 
whilst  those  which  are  very  active  would  be  widely  diffused. 
Precisely  the  reverse  of  this  is  actually  the  case.     The  com- 
mon oyster  extends  at  least  from  the  St.  Lawrence  to  the 
Carolinas  ;  its  range  is  consequently  very  great ;  much  more 
so  than  that  of  some  of  the  fleet  animals,  as,  for  instance,  the 
Moose.     It  is  even  probable  that  the  very  inability  of  the 
oyster  to  travel  really  contributes  to  its  diffusion,  inasmuch 
as,  having  once  spread  over  extensive  grounds,  there  is  no 
chance  of  its  return  to  a  former  limitation,  inasmuch  as,  being 
fixed,  and   consequently  unable  to  choose   positions  for  its 
eggs,  they  must  be   left  to  th^   mercy  of  currents ;  while 
Fishes,  by  depositing  their  eggs  in  the  bays  and  inlets  of  the 
shore,  undisturbed  by  currents  and  winds,  secure  them  from 
too  wide  a  dispersion. 

406.  The  nature  of  their  food  has  an  important  bearing 
upon  the  grouping  of  animals,  and  upon  the  extent  of  their 
distribution.     Carnivorous  animals  are  generally  less  con- 
fined in  their  range  than  herbivorous  ones  ;  because  their 
food  is  almost  every  where  to  be  found.     The  herbivora,  on 
the   contrary,  are    restricted   to  the    more   limited    regions 
Co/responding  to   the   different   zones   of  vegetation.     The 
same  remark  may  be  made  with  respect  to  Birds.     Birds  of 
prey,  such  as  the  eagle  and  vulture,  have  a  mich  wider  range 
than  the  granivorous  and  gallinaceous  birds.     Still,  notwith- 
standing the  facilities  they  have  for  change  of  place,  even 
the  birds  tl  at  wander  widest  recognize  limits  which  they  do 


GENERAL    LAWS    OF    DISTRIBUTION.  191 

not  overstep.  The  Condor  of  the  Cordilleras  does  not  do 
scend  into  the  temperate  regions  of  the  United  States  ;  and  yet 
it  is  not  that  he  fears  the  cold,  since  he  is  frequently  known 
to  ascend  even  above  the  highest  summits  of  the  Andes,  and 
disappears  from  view  where  the  cold  is  most  Intense.  Nor 
can  it  be  from  lack  of  piey. 

407.  Again,  the  peculiar  configuration  of  a  country  some- 
times determines  a  peculiar  grouping  of  animals,  into  what 
may  be  called  local  faunas.     Such,  for  example,  are  the 
prairies  of  the  West,  the  Pampas  of  South  America,  the 
Steppes  of  Asia,  the  Deserts  of  Africa  ;  —  and,  for  marine 
an-mals,  the  basin  of  the  Caspian.     In  all  these  localities, 
animals  are  met  with  which  exist  only  there,  and  are  not 
found  except  under  those  particular  conditions. 

408.  Finally,  to  obtain  a  true  picture  of  the  zoological 
distribution  of  animals,  not  the  terrestrial  types  alone,  but 
the  marine  species,  must  also  be  included.     Notwithstanding 
the  uniform  nature  of  the  watery  element,  the  animals  which 
dwell  in  it  are  not  dispersed  at  random  ;   and  though  the 
limits  of  the  marine  may  be  less  easily  defined  than  those  of 
the  terrestrial  faunas,  still,  marked  differences  between  the 
animals  of  great  basins  are  not  less  observable.     Properly 
to  apprehend  how  marine   animals  may  be  distributed  into 
local  faunas,  it  must  be  remembered  that  their  residence  is 
not  in  the  high  sea,  but  along  the  coasts  of  continents  and 
on  soundings.     It  is  on  the  Banks  of  Newfoundland,  and  not 
in  the  deep  sea,  that  the  great  cod-fishery  is  carried  on  ;  and 
it  is  well  known  that  when  fishes  migrate,  they  run  along  the 
shores.     The  range  of  marine  species  being,  therefore,  con- 
fined to  the  vicinity  of  the  shores,  their  distribution  must  be 
subjected  to  laws  similar  to  those  which  regulate  the  terres- 
trial faunas.     As  to  the  fresh-water  fishes,  not  only  do  the 
species  vary  in  the  different  zones,  but  even  the  different 
rivers  of  the  same  region  have  species  peculiar  to  them,  and 


192  GEOGRAPHICAL    DISTRIBUTION    OF    ANIMALS. 

not  found  in  neighboring  streams.  The  garpikes  (Lepi- 
dosteus)  of  the  American  riveVs  afford  a  striking  example  ol 
this  kind. 

409.  A  very  influential  cause  in  the  distribution  of  aquatic 
animals  is  the  depth  of  the  water;  so  that  several  zoological 
zones,  receding  from  the  shore,  may  be  defined,  according 
to  the  depth  of  water ;  much  in  the  same  manner  as  we  mark 
different   zones   at  different  elevations  in   ascending    moun- 
tains, (398.)     The  Mollusks,  and  even  the  Fishes  found  near 
the  shore   in  shallow  water,  differ,  in  general,  from  those 
living  at  the  depth  of  twenty  or  thirty  feet,  and  these  again 
are  found  to  be  different  from  those  which  are  met  with  at 
a  greater  depth.     Their  coloring,  in  particular,  var  es,  ac- 
cording to  the  quantity  of  light  they  receive,  as  has  also 
been  shown  to  be  the  case  with  the  marine  plants. 

410.  It  is  sometimes  the  case  that  one  or  more  animals 
are  found  upon  a  certain  chain  of  mountains,  and  not  else- 
where ;  as,  for  instance,  the  Mountain  Sheep  (Ovis  montana) 
upon  the  Rocky  Mountains,  or  the  Chamois  and  the  Ibex 
upon  the  Alps.     The  same  is  also  the  case  on  some  of  the 
wide    plains  or  prairies.     This,  however,  does   not   entitle 
such  regions  to  be   considered  as  having  an   independent 
fauna,  any  more  than  a  lake  is  to  be  regarded  as  having  a 
peculiar  fauna,  exclusive  of  the  animals  of  the  surrounding 
country,  merely  because  some  of  the  species  found  in  the 
lake  may  not  ascend  the  rivers  emptying  into  it.     It  is  only 
when  the  whole  group  of  animals  inhabiting  such  a  region 
has  such  peculiarities  as  to  give  it  a  distinct  character,  when 
contrasted  with  animals  found  in  surrounding  regions,  that 
it  is  to  be  regarded  as  a  separate  fauna.     Such,  for  exam- 
p.e,  is  the  fauna  of  the  great  steppe,  or  plain  of  Gobi,  in 
Asia  ;  and  such  indeed  that  of  the  chain  of  the  Rocky  Moun- 
tains may  prove  to  be,  when  the  animals  inhabiting  them  shall 
bt-  batter  known. 


GENERAL    LAWS    OF    DISTRIBUTION.  193 

411.  The  migration  of  animals  might  at  first  seem  to  pre- 
sent a  serious  difficulty  in  determining  the  character  or  the 
limits  of  a  fauna ;  but  this  difficulty  ceases,  if  we  regard  the 
country  of  an  animal  to  be  the  place  where  it  makes  its 
nabitual  abode.     As  to  Birds,  which  of  all  animals  wander 
farthest,  it  may  be   laid  down  as  a  rule,  that  they  belong 
to  the  zone  in  which  they  breed.     Thus,  the  gulls,  many  of 
the    ducks,   mergansers,   and   divers,  belong  to  the  boreal 
regions,  though  they  pass  a  portion  of  the  year  with  us.    On 
the  other  hand,  the  swallows  and  martins,  and  many  of  the 
gallinaceous  birds  belong  to  the  temperate  faunas,  notwith- 
standing their  migration  during  winter  to  the  confines  of  the 
torrid  zone.     This  rule  does  not  apply  to  the  fishes  who  an- 
nually leave  their  proper  home,  and  migrate  to  a  distant 
region  merely  for  the  purpose  of  spawning.     The  Salmon-, 
for  example,  comes  down  from  the  North,  to  spawn  on  the 
coast  of  Maine  and  Nova  Scotia. 

412.  Few  of  the  Mammals,  and  these  mostly  of  the  tribe 
of  Rodents,  make  extensive  migrations.     Among  the  most 
remarkable  of  these  are  the  Kamtschatka  rats.     In  Spring 
they  direct  their  course  westward,  in  immense  troops  ;  and, 
after  a  very  long  journey,  return  again  in  Autumn  to  their 
quarters,  where  their  approach  is  anxiously  awaited  by  the 
hunters,  on  account  of  the  fine  furs  to  be  obtained  from  the 
numerous   carnivora  which   always   follow   in    their    train. 
The  migrations  of  the  Lemmings  are  marked  by  the  devas- 
tations they  commit  along  their  course,  as  they  come  down 
from  the  borders  of  the   Frozen  Ocean  to  the  valleys  of 
Lapland  ard  Norway ;  but  their  migrations  are  not  period* 
ical. 

17 


194  GEOGRAPHICAL    DISTRIBUTION  'oF   ANIMALS. 


SECTION  II 

DISTRIBUTION    OF    THE    FA'JNAS 

413.  We  have  stated  that  all  the  faunas  of  the  globe  may 
be  divided  into  three  groups,  corresponding  to  as  manygreal 
climatal  divisions,  namely,  the  glacial  or  arctic,  the  temperate 
and  the  tropical  faunas.     These  three  divisions  appertain  to 
both  hemispheres,  as  we  recede  from  the  equator  towards  the 
north  or  south  poles.     It  will  hereafter  be  shown  that  the 
tropical   and  temperate  faunas  may  be   again  divided  into 
several  zoological  provinces,  depending  on  longitude  or  on 
the  peculiar  configuration  of  the  continents. 

414.  No  continent  is  better  calculated  to  give  a  correc' 
idea  of  distribution  into  faunas,  as  determined  by  climate 
than  the  continent  of  America ;  extending  as  it  does  across 
both  hemispheres,  and  embracing  all  latitudes,  so  that  all 
climates  are  represented  upon  it,  as  shown  by  the  chart  on  the 
following  page. 

415.  Let  a  traveller  embark  at  Iceland,  which  is  situated 
on  the  borders  of  the  polar  circle,  with  a  view  to  observe, 
in  a  zoological  aspect,  the  principal  points  along  the  eastern 
shore  of  America.     The  result  of  his  observation  will   be 
very  much  as  follows.     Along  the  coast  of  Greenland  and 
Iceland,  and  also  along  Baffin's  Bay,  he  will  meet  with  an 
unvaried  fauna,  composed  throughout  of  the  same  animals, 
which  are  also  for  the  most  part  identical  with  those  of  the 
arctic  shores  of  Europe.     It  will  be  nearly  the  same  along 
the  coast  of  Labrador. 

416.  As  he  approaches  Newfoundland,  he  will  see  the 
landscape,  and  with  it  the  fauna,  assuming  a  somewhat  more 
varied  aspect.     To  the  wide  and  naked  or  turfy  plains  of 
the  boreal  regions  succeed   forests,  in  which  he  will   find 


© 

N.POLE 


I. 

II. 
III. 
IV. 

V. 
VI. 


FAUNAS. 

North  Glacial  or  Arctic. 
Northern  Temperate. 
Northern  Warm. 
Tropical. 
Southern  Warm. 
Southern  Temperate. 


196  GEOGRAPHICAL    DISTRIBUTION    OF   ANIMALS. 

various  animals  which  dwell  only  in  forests.  Here  the  tem- 
perate fauna  commences.  Still  the  number  of  species  is  not 
5Tet  very  considerable  ;  but  as  he  advances  southward,  along 
the  coasts  of  Nova  Scotia  and  New  England,  he  finds  new 
species  gradually  introduced,  while  those  of  the  colder  regions 
diminish,  and  a*  length  entirely  disappear,  some  few  acci- 
dental or  periodical  visitors  excepted,  who  wander,  during 
winter,  as  far  south  as  the  Carolinas. 

417.  But  it  is  after  having  passed  the  boundaries  of  the 
United  States,  among  the  Antilles,  and  more  especially  on 
the  southern  continent,  along  the  shores  of  the  Orinoco  and 
the  Amazon,  that  our  traveller  will  be  forcibly  struck  with 
the  astonishing  variety  of  the  animals  which  people  the  for- 
ests, the  prairies,  the  rivers,  and  .the  sea-shores,  most  of  which 
he  will  also  find  to  be  different  from  those  of  the  northern 
continent.     By  this  extraordinary  richness  of  new  forms,  he 
will  become  sensible  that  he  is  now  in  the  domain  of  the 
tropical  fauna. 

418.  Let  him  still  travel  on  beyond  the  equator  towards 
the  tropic  of  Capricorn,  and   he  will   again  find  the  scene 
change  as  he  enters  the  regions  where  the  sun  casts  his  rays 
more  obliquely,  and  where  the  contrast  of  the  seasons  is 
more  marked.     The  vegetation  will  be  less  luxuriant;  the 
palms  will  have  disappeared  to  make  place  for  other  trees ; 
the  animals  will  be  less  varied,  and  the  whole  picture  will 
recall  to  him,  in  some  measure,  what  he  witnessed  in  the 
United  States.     He  will  again  find  himself  in  the  temperate 
region,  and  this  he  will  trace  on,  till  he  arrives  at  the  ex- 
tremity of  the  continent,  the  fauna  and  the  flora  becoming 
more  and  more  impoverished  as  he  approaches  Cape  Horn. 

419.  Finally,  we  know  that  there  is  a  continent  around 
the  South  Pole.     Although  we  have  as  yet  but  very  imper- 
fect notions  respecting  the  animals  of  this  inhospitable  clime 
still,  the  few  which  have  already  been  observed  there  present 


DISTRIBUTION    OF    THE    FAUNAS.  197 

a  close  analogy  to  those  of  the  arctic  region.  It  is  another 
glacial  fauna,  namely,  the  antarctic.  Having  thus  sketched 
the  general  divisions  of  the  faunas,  it  remains  to  point  out 
the  principal  features  of  each  of  them. 

420.  I.  ARCTIC  FAUNA.  —  The  predominant  feature  of  the 
Arctic  Fauna  is  its  uniformity.  The  species  are  few  in  num- 
ber ;  but,  on  the  other  hand,  the  number  of  individuals  is 
immense.  We  need  only  refer  to  the  clouds  of  birds  which 
hover  upon  the  islands  and  shores  of  the  North  ;  the  shoals 
of  fishes,  the  salmon  among  others,  which  throng  the  coasts 
of  Greenland,  Iceland,  and  Hudson's  Bay.  There  is  great 
uniformity,  also,  in  the  form  and  color  of  these  animals,  Not 
a  single  bird  of  brilliant  plumage  is  found,  and  few  fishes 
with  varied  hues.  Their  forms  are  regular,  and  their  tints 
as  dusky  as  the  northern  heavens.  The  most  conspicuous 
animals  are  the  white-bear,  the  moose,  the  reindeer,  the 
musk-ox,  the  white-fox,  the  polar-hare,  the  lemming,  and 
various  Seals  ;  but  the  most  important  are  the  Whales,  which, 
it  is  to  be  remarked,  rank  lowest  of  all  the  Mammals. 
Among  the  Birds  may  be  enumerated  some  sea-eagles  and 
a  few  Waders,  while  the  great  majority  are  aquatic  species, 
such  as  gulls,  cormorants,  divers,  petrels,  ducks,  geese,  gan- 
nets,  &c.,  all  belonging  to  the  lowest  orders  of  Birds.  Rep- 
tiles are  altogether  wanting.  The  Articulata  are  represented 
by  numerous  marine  worms,  and  by  minute  crustaceans  of 
the  orders  Isopoda  and  Amphipoda.  Insects  are  rare,  and 
of  inferior  types.  Of  the  type  of  Mollusks,  there  are 
Acephala,  particularly  Tunicata,  fewer  Gasteropods,  and 
very  few  Cephalopods.  Among  the  Radiata  are  a  great 
number  of  jelly-fishes,  particularly  the  Beroe  ;  and  to  con- 
clude with  the  Echinoderms,  there  are  several  star-fishes 
and  Echini,  but  few  Holothurise.  The  class  of  Polypi  is 
very  scantily  represented,  and  those  producing  stony  corals 
are  entirely  wan  ing. 


198  GEOGBAPHICAL    DISTRIBUTION    OF    ANIMALS. 

421.  This  assemblage  of  animals  is  evidently  inferior  to 
that  of  other  faunas,  especially  to  those  of  the  tropics.     Not 
that  there  is  a  deficiency  of  animal  life  ;  for  if  the  species 
are  less  numerous,  there  is  a  compensation  in  the  multitude 
of  individuals,  and,  also,  in  this  other  very  significant  fact, 
that  the  largest  of  all  animals,  the  whales,  belong  to  this 
fauna. 

422.  It  has  already  been  said,  (400,)  that  the  arctic  fauna 
of  the  three  continents  is  the  same ;  its  southern  limit,  how- 
ever, is  not  a  regular  line.    It  does  not  correspond  precisely 
with  the  polar  circle,  but  rather  to  the  isothermal  zero  •  that 
is,  the  line  where  the  average  temperature  of  the  year  is  at 
32°  of  Fahrenheit.     The  course  of  this  line  presents  numer- 
ous undulations.    In  general,  it  may  be  said  to  coincide  with 
the  northern  limit  of  trees,  so  that  it  terminates  where  forest 
vegetation  succeeds  the  vast  arid  plains,  the  barrens  of  North 
America,  or  the  tundras  of  the  Samoyedes.     The  uniformity 
of  these  plains  involves  a  corresponding  uniformity  of  plants 
and  animals.     On  the  North  American  continent  it  extends 
much  farther  southward  on  the  eastern  shore  than  on  the 
western.     From   the  peninsula  of  Alashka,  it  bends  north- 
wards towards  the  Mackenzie,  then  descends  again  towards 
the  Bear  Lake,  arid  comes  down  nearly  to  the  northern  shore 
of  Newfoundland. 

423.  II.  TEMPERATE  FAUNAS.  —  The  faunas  of  the  tern- 
pei ate  regions  of  the  northern  hemisphere  are  much  more 
varied   than  that  of  the  arctic  zone.     Instead  of  consisting 
mainly  of  aquatic  tribes,  we  have  a  considerable  number  of 
terrestrial  animals,  of  graceful  form,  animated  appearance, 
and  varied  colors,  though  less  brilliant  than  those  found  in 
tropical  regions.     Those  parts  of  the  country  covered  with 
forests  especially  swarm  with  insects,  which  become  the  food 
of  other  animrls  ;  worms  and  terrestrial  and   flip-iadle  mol- 

usks  are  also  ibundant. 


DISTRIBUTION    OF    THE    FAUNAS.  199 

424.  Still,  the  climate   is  not  sufficiently  warm  over  the 
whole  extent  of  this  zone  to  allow  the  trees  to  retain  their 
foliage   throughout  the  year.      At  its  northern  margin,  the 
leaves,  excepting  those  of  the  pines  and  spruces,  fall,  on  the 
approach  of  the  cold  season,  and  vegetation  is  arrested  for  a 
lunger  or  shorter  period.     Insects  retire,  and   the  animals 
which  live  upon  them  no  longer  find  nourishment,  and  are 
ohliged  to  migrate  to  warmer  regions,  on  the  borders  of  the 
tropics,  where,  amid  the  ever-verdant  vegetation,  they  find 
fbe  means  of  subsistence. 

425.  Some  of  the  herbivorous   Mammals,  the  Bats,  and 
the  reptiles  which  feed  on  insects,  pass  the  winter  in  a  state 
of  torpor,  from  which  they  awake  in  spring.     Others  retire 
into  dens,  and  live  on  the  provisions  they  have  stored  up 
during  the  warm  season.     The  Carnivora,  the  Ruminants, 
and  the  most  active  portion  of  the  Rodents,  are  the  only  ani- 
mals that  do  not  change  either  their  abode  or  their  habits. 
The  fauna  of  the    temperate    zone    thus  presents  an  ever- 
changing  picture,  which  may  be  considered  as  one  of  its 
most  important  features,  since  these  changes  recur  with  equal 
constancy  in  the  Old  and  the  New  World. 

426.  Taking  the  contrast  of  the  vegetation  as  a  basis,  and 
the  consequent  changes  of  habit  imposed  upon  the  denizens 
of  the  forests,  the  temperate  fauna  has  been  divided  into 
two  regions ;  a  northern  one,  where  the  trees,  except  the 
pines,  drop  their  leaves  in  winter,  and  a  southern  one,  where 
they  are  evergreen.     Now,  as  the  limit  of  the  former,  that 
of  the  deciduous  trees,  coincides,  in  general,  with  the  limit 
of  the  pines,  it  may  be  said  that  the  cold  region  of  the  tem- 
perate fauna  extends  as  far  as  the  pines.     In  the  United 
States  this  coincidence  is  not  so  marked  as  in  other  regions, 
inasmuch  as  the  pines  along  the  Atlantic  coast  extend  into 
Florida,  while  they  do  not  prevail  in  the  Western  States  ; 
but  we  may  consider  as  belonging  to  the  southern  portion 


200  GEOGRAPHICAL    DISTRIBUTION    OF    ANIMALS. 

of  the  temperate  region  that  part  of  the  country  south  of 
the  la  itude  where  the  Palmetto'or  Cabbage-tree  (Chanuzrops) 
commences,  namely,  all  the  States  to  the  south  of  North 
Carolina ;  while  the  States  to  the  north  of  this  limit  belong 
to  the  northern  portion  of  the  temperate  region. 

427.  This  division  into  two  zones  is  supported  by  obser- 
vations made  on  the  maritime  faunas  of  the  Atlantic  coast 
The  line  of  separation  between  them,  however,  being  influ 
enced-  by  the  Gulf  Stream,  is  considerably  farther  to  the 
north,  namely,  at  Cape  Cod  ;  although  there  is  also  another 
decided  limitation  of  the   marine  animals  at  a  point  nearly 
coinciding  with  the  line  of  demarkation  above  mentioned, 
namely,  at  Cape  Hatteras.     It  has  been  observed   that  of 
one  hundred  and  ninety-seven  Mollusks  inhabiting  the  coast 
of  New  England,  fifty  do  not  pass  to  the  north  of  Cape  Cod, 
and  eighty-three  do  not  pass  to  the  south  of  it ;  only  sixty- 
four  being  common  to  both  sides  of  the  Cape.     A  similar 
limitation  of  the  range  of  Fishes  has  been  noticed  by  Dr. 
Storer  ;  and   Dr.  Holbrook   has  found  the  Fishes  of  South 
Carolina  to  be  different  from  those  of  Florida  and  the  West 
Indies.     In  Europe,  the  northern  part  of  the  temperate  re- 
gion extends  to  the  Pyrenees  and   the  Alps ;  and  its  south- 
ern portion  consists  of  the   basin  of  the  Mediterranean,  to- 
gether with  the  northern  part  of  Africa,  as  far  as  the  desert 
of  Sahara. 

428.  A  peculiar  characteristic  of  the  faunas  of  the  tem- 
perate regions  in  the  northern  hemisphere,  when  contrasted 
with  those  of  the  southern,  is  the  great  similarity  of  the  pre- 
vailing types  on  both  continents.     Notwithstanding  the  5m- 
liiense  extent  of  country  embraced,  the  same  stamp  is  every 
where  exhibited.     Generally,  the  same  families,  frequently 
chs    same    genera,    represented    by    different   species,    are 
found.     There  are  even  a  few  species  of  terrestrial  animals 
regarded  as    identical   on   the  continents  of   Europe   and 


DISTRIBUTION  OF  THE  FAUNAS.  201 

America  ;  but  their  supposed  number  is  constantly  dimin- 
ished, as  more  accurate  observations  are  made.  The  pre- 
dominant types  among  the  mammals  are  the  bison,  deer,  ox 
horse,  hog,  numerous  rodents,  especially  squirrels  and  hares, 
nearly  all  the  insectivora,  weasels,  martens,  wolves,  foxes., 
wildcats,  &c.  On  the  other  hand,  there  are  no  Edentata 
and  no  Quadrumana,  with  the  exception  of  some  monkeys, 
on  the  two  slopes  of  the  Atlas  and  in  Japan.  Among  Birds, 
there  is  a  multitude  of  climbers,  passerine,  gallinaceous,  and 
many  rapacious  birds.  Of  Reptiles,  there  are  lizards  and 
tortoises  of  small  or  medium  size,  serpents,  and  many  ba- 
trachians,  but  no  crocodiles.  Of  fishes,  there  is  the  trout 
family,  the  cyprinoids,  the  sturgeons,  the  pikes,  the  cod,  and 
especially  the  great  family  of  Herrings  and  Scomberoids,  to 
which  latter  belong  the  mackerel  and  the  tunny.  All  classes 
of  the  Mollusks  are  represented  ;  though  the  cephalopods  are 
less  numerous  than  in  the  torrid  zone.  There  is  an  infinite 
number  of  Articulata  of  every  type,  as  well  as  numerous 
Polyps,  though  the  corals  proper  do  not  yet  appear  abun- 
Jantly. 

429.  On  each  of  the  two  continents  of  Europe  and  Amer- 
ica there  is  a  certain  number  of  species,  which  extend  from 
one  extreme  of  the  temperate  zone  to  the  other.  Such,  for 
example,  are  the  deer,  the  bison,  the  cougar,  the  flying-squir- 
rel, numerous  birds  of  prey,  several  tortoises,  and  the  rattle- 
snake, in  America.  In  Europe,  the  brown  bear,  wolf, 
swallow,  and  many  birds  of  prey.  Some  species  have  a 
still  wider  range,  like  the  ermine,  which  is  found  from  Behr- 
ing's  Straits  to  the  Himalaya  Mountains,  that  is  to  say,  from 
the  coldest  regions  of  the  arctic  zone  to  the  southern  confines 
of  the  temperate  zone.  It  is  the  same  with  the  muskrat, 
which  is  found  from  the  mouth  of  Mackenzie's  River  to 
Florid  i.  The  field-mouse  has  an  equal  range  in  Europe, 
Other  species,  on  the  contrary,  are  limited  to  one  region 


202  GEOGRAPHICAL    DISTRIBUTION    OF    ANIMALS. 

The  Canadian  elk  is  confined  to  the  northern  portion  of  the 
fauna ;  while  the  prairie  wolf,  the  fox-squirrel,  the  Bassaris, 
and  numerous  birds,  never  leave  the  southern  portion.* 

430.  In  America,  as  in  the   Old  World,  the  temperate 
fauna  is  further  subdivided  into  several  districts,  which  may 
be  regarded  as  so  many  zoological  provinces,  in  each  of 
which  there  is  a  certain  number  of  animals  differing  from 
(hose  in  the  others,  though  very  closely  allied.     Temperate 
America  presents  us  with  a  striking  example  in  this  respect. 
We  have,  on  the  one  hand : 

1st.  The  fauna  of  the  United  States  properly  so  called,  on 
this  side  of  the  Rocky  Mountains. 

2d.  The  fauna  of  Oregon  and  California,  beyond  those 
mountains. 

Though  there  are  some  animals  which  traverse  the  chain 
of  the  Rocky  Mountains,  and  are  found  in  the  prairies  of 
the  Missouri  as  well  as  on  the  banks  of  the  Columbia,  as, 
for  example,  the  Rocky  Mountain  deer,  (Antilope  furcifer,} 
yet,  if  we  regard  the  whole  assemblage  of  animals,  they  are 
found  to  differ  entirely.  Thus,  the  rodents,  part  of  the 
ruminants,  the  insects,  and  all  the  mollusks,  belong  to  dis- 
tinct species. 

431.  The  faunas  or  zoological  provinces  of  the  Old  World 
which  correspond  to  these  are  : 

*  The  types  which  are  peculiar  to  temperate  America,  and  are  not  found 
in  Europe,  are  the  Opossum,  several  genera  of  Insectivora,  among  them 
the  shrew-mole  (Scalops  aquaticus)  and  the  star-nose  mole,  (Gondylura 
cristata,)  which  replaces  the  Mygale  of  the  Old  World ;  several  genera 
of  rodents,  especially  the  muskrat.  Among  the  types  characteristic  of 
America  must  also  be  reckoned  the  snapping-turtle  among  the  tortoises ; 
the  Menobranchus  and  Menopoma,  among  the  Salamanders ;  the  Gar- 
pike  and  Amia  among  the  fishes ;  and  finally,  among  the  Crustacea,  the 
Limulus  Among  the  types  which  are  wanting  in  temperate  America, 
and  which  are  found  in  Europe,  may  be  cited  the  horse,  the  wild  boar,  and 
the  true  mouse.  All  the  species  of  domestic  mice  which  live  in  America 
have  been  br  )ught  from  the  Old  World 


DISTRIBUTION    OF    THE    FAUNAS.  203 

1st.  The  fauna  of  Europe,  which  is  very  closely  related  to 
that  of  the  United  States  proper. 

2d.  The  fauna  of  Siberia,  separated  from  the  fajna  of 
Europe  by  the  Ural  Mountains. 

3d.  The  fauna  of  the  Asiatic  table-land,  which,  from  what 
is  as  yet  known  of  it,  appears  to  be  quite  distinct. 

4th.  The  fauna  of  China  and  Japan,  which  is  analogous 
to  that  of  Europe  in  the  Birds,  and  to  that  of  the  United 
States  i*  the  Reptiles  —  as  it  it  also  in  the  flora. 

Lastly,  it  is  in  the  temperate  zone  of  the  northern  hemi- 
sphere that  we  meet  with  the  most  striking  example  of 
those  local  faunas  which  have  been  mentioned  above. 
Such,  for  example,  is  the  fauna  of  the  Caspian  Sea,  of  the 
steppes  of  Tartary,  and  of  the  Western  prairies. 

432.  The  faunas  of  the  southern  temperate  regions  differ 
from  those  of  the  tropics  as  much  as  the  northern  temperate 
fauna?  do ;  and,  like  them  also,  may  be  distinguished  into 
two  provinces,  the  colder  of  which  embraces  Patagonia. 
But  besides  differing  from  the  tropical  faunas,  they  are  also 
quite  unlike  each  other  on  the  different  continents.  Instead 
of  that  general  resemblance,  that  family  likeness  which  we 
have  noticed  between  all  the  faunas  of  the  temperate  zone 
of  the  northern  hemisphere,  we  find  here  the  most  complete 
contrasts.  Each  of  the  three  continental  peninsulas  which 
jut  out  southerly  into  the  ocean  represents,  in  some  sense,  a 
separate  world.  The  animals  of  South  America,  beyond  the 
tropic  of  Capricorn,  are  in  all  respects  different  from  those 
at  the  southern  extremity  of  Africa.  The  hyenas,  wild- 
boars,  and  rhinoceroses  of  the  Cape  of  Good  Hope  have  no 
analogues  on  the  American  continent;  and  the  difference  is 
equally  great  between  the  birds,  reptiles  and  fishes,  insects 
and  mo.iusks.  Among  the  most  characteristic  animals  of 
the  south  irn  extremity  of  America  are  peculiar  species  of 
seals  and  especially,  among  aquatic  birds,  the  penguins. 


204  GEOGRAPHICAL    DISTRIBUTION    OF    ANIMALS. 

433.  New  Holland,  with   its    marsupial    mammals,  with 
which  are  associated  insects  and  mollusks  no  less  singulai 
furnishes  a  fauna  still  more  peculiar,  and  which  has  no  sinri 
larity  to  those  of  any  of  the  adjacent  countries.     In  the  seas 
of  that  continent,  where  every  thing  is  so  strange,  we  find 
the  curious  shark,  with  paved  teeth  and  spines  on  the  back, 
(Cestracion  Philippii,)  the  only  living  representative  of  a 
family  so  numerous  in  former  zoological  ages.     But  a  most 
remarkable   feature   of  this  fauna   is,  that  the  same  types 
prevail  over  the  whole  continent,  in  its  temperate  as  well  as 
its  tropical  portions,  the  species  only  being  different  at  dif- 
ferent localities. 

434.  TROPICAL  FAUNAS. — The   tropical  faunas  are   dis- 
tinguished, on  all  the  continents,  by  the  immense  variety  of 
animals  which  they  comprise,  not  less  than  by  the  brilliancy 
of  their  dress.     All   the  principal  types  of  animals  are  rep- 
resented,  and   all   contain    numerous   genera   and    species. 
We  need  only  refer  to  the  tribe  of  humming-birds,  which 
numbers  not  less  than  300  species.     It  is  very  important  to 
notice,  that  here  are  concentrated  the  most  perfect,  as  well 
as  the  oddest,  types  of  all  the  classes  of  the  Animal  King- 
dom.    The  tropical  region  is  the  only  one  occupied  by  the 
Quadrumana,  the  herbivorous  bats,  the  great  pachydermata, 
such  as  the  elephant,  the  hippopotamus,  and  the  tapir,  and 
the  whole   family  of  Edentata.     Here  also  are   found   the 
largest  of  the  cat  tribe,  the  lion  and  tiger.     Among  the  Birds 
we   may   mention   the    parrots  and   toucans,  as   essentially 
tropical ;   among  the    Reptiles,  the    largest   crocodiles,  and 
gigantic  tortoises  ;  and  finally,  among  the  articulated  animals, 
an    immense   variety  of  the    most  beautiful   insects.     The 
marine  animals,  as  a  whole,  are  equally  superior  to  those  of 
other  regions  ;  the  seas  teem  with  crustaceans  and  numerous 
cephalopods,  together  with  an  infinite  variety  of  gasteropods 
and  acephala.     The  Echinoderms  there  attain  a  magnitude 


DISTRIBUTION    OF    THE    FAUNAS.  205 

and  variety  elsewhere  unknown  ;  and  lastly,  the  Po'yps  there 
display  an  activity  of  which  the  other  zones  present  no  ex- 
ample. Whole  groups  of  islands  are  surrounded  with  coral 
reefs  formed  by  those  little  animals. 

435.  The  variety  of  the  tropical  fauna  is  further  enriched 
by  the  circumstance  that  each  continent  furnishes  new  and 
peculiar  forms.     Sometimes  whole  types  are  limited  to  one 
continent,  as  the  sloth,  the  toucans,  and  the  humming-birds  to 
America,  the  giraffe  and  hippopotamus  to  Africa ;  and  again 
animals  of  the  same  group  have  different  characteristics,  ac- 
cording as  they  are  found  on  different  continents.      Thus, 
the  monkeys  of  America   have   flat   and  widely  separated 
nostrils,  thirty-six  teeth,  and  generally  a  long,  prehensile  tail. 
The  monkeys  of  the  Old  World,  on  the  contrary,  have  nostrils 
close  together,  only  thirty-two  teeth,  and  not  one  of  them  has 
a  prehensile  tail. 

436.  But  these  differences,  however  important  they  may 
appear  at  first  glance,  are  subordinate  to  more  important 
characters,  which  establish  a  certain  general  affinity  between 
all  the  faunas  of  the  tropics.     Such,  for  example,  is  the  fact 
that  the  quadrumana  are  limited,  on  all  the  continents,  to 
the  warmest  regions ;  and  never,  or  but  rarely,  penetrate 
into  the  temperate  zone.     This  limitation^  a  natural  con- 
sequence of  the  distribution  of  the  palms  ;  for  as  these  trees, 
which  constitute  the  ruling  feature  of  the  flora  of  the  tropics, 
furnish,  to  a  great  extent,  the  food  of  the  monkeys  on  both 
continents,  we  have  only  to  trace  the  limits  of  the  palms,  to 
have  a  pretty  accurate  indication  of  the  extent  of  the  tropical 
faunas  on  all  three  continents. 

437.  Several  well-marked  faunas  may  be  distinguished  in 
the  tropical  part  of  the  American  continent,  namely : 

1.  The  fauna  of  Brazil,  characterized  by  its  gigantic  rep- 
tiles, its  monkeys,  its  Edentata,  its  tapir,  its  humming-buds, 
and  its  astonishing  variety  of  insects. 
18 


206  GEOGRAPHICAL    DISTRIBUTION    OF    ANIMALS. 

2.  The   fauna  of  the  western  slope  of  the  Andes,  com- 
prising Chili  and   Peru ;  and   distinguished   by  its  Llamas, 
vicunas,  and  birds,  which  differ  from  those  of  the  basin  of 
the  Amazon,  as  also  do  the  insects  and  mollusks. 

3.  The  fauna  of  the  Antilles  and   the  Gulf  of  Mexido. 
This  is  especially  characterized  by  its  marine  animals,  among 
which  the  Manatee  is  particularly  remarkable  ;  an   infinite 
variety  of  singular  fishes,  embracing  a  large   number  of 
Plectognaths  ;  also  Mollusks,  and  Radiata  of  peculiar  species. 
[t  is  in  this  zone  that  the  Pentacrinus  caput-medusa  is  found, 
the  only  representative,  in  the  existing  creation,  of  a  family  so 
numerous  in  ancient  epochs,  the  Crinoidea  with  a  jointed  stem. 

The  limits  of  the  fauna  of  Central  America  cannot  yet  be 
well  defined,  from  want  of  sufficient  knowledge  of  the  ani- 
mals which  inhabit  those  regions. 

438.  The  tropical  zone  of  Africa  is  distinguished  by  a 
striking  uniformity  in  the  distribution  of  the  animals,  which 
corresponds  to  the  uniformity  of  the  structure  and  contour 
of  that  continent.  Its  most  characteristic  species  are  spread 
over  the  whole  extent  of  the  tropics :  thus,  the  giraffe  is  met 
with  from  Upper  Egypt  to  the  Cape  of  Good  Hope.  The 
hippopotamus  is  found  at  the  same  time  in  the  Nile,  the 
Niger,  and  Orange  River.  This  wide  range  is  the  more 
significant  as  it  also  relates  to  herbivorous  animals,  and  thus 
supposes  conditions  of  vegetation  very  similar,  over  wide 
countries.  Some  forms  are,  nevertheless,  circumscribed 
within  narrow  districts  ;  and  there  are  marked  differences 
between  the  animals  of  the  eastern  and  western  shores. 
Among  the  remarkable  species  of  the  African  torrid  region 
are  the  baboons,  the  African  elephant,  the  crocodile  of  the 
Nile,  a  vast  number  of  Antelopes,  and  especially  two  species 
of  Orang-outang,  the  Chimpanzee  and  the  Engeena,  a  large 
and  remarkable  animal,  only  recently  described.  The  fishes 
of  the  N'le  have  a  tropical  character,  as  well  as  the  animals 


CONCLUSIONS.  207 

of  Arabia,  which  are  more  allied  to  those  of  Africa  tl  \n  tc 
those  of  Asia. 

439.  The   tropical    fauna  of  Asia,  comprising   the   two 
peninsulas  of  India  and  the  Isles  of  Sunda,  is  not  less  marked. 
It  is  the  country  of  the  gibbons,  the  red  orang,  the  royal 
tiger,  the  gavial,  and  a  multitude  of  peculiar  birds.     Among 
the   fishes,  the   family  of  Chetodons   is    most   numerously 
represented.       Here    also    are    found    those    curious   spiny 
fishes,  whose  intricate  gills  suggested  the  name  Labyrinthici, 
by  which  they  are  known.     Fishes  with  tufted  gills  are  more 
numerous  here  than  in  other  seas.     The  insects  and  mol- 
lusks  are  no  less  strongly  characterized.     Among  others  is 
the  nautilus,  the  only  living  representative  of  the  great  fam- 
ily of  large,  chambered-shells  which  prevailed  so  extensively 
over  other  types,  in  former  geological  ages. 

440.  The  large   Island   of  Madagascar  has   its   peculiai 
fauna,  characterized   by  its  makis  and   its  curious  rodents. 
It  is  also  the  habitat  of  the  Aya-aya.     Polynesia,  exclusive 
of  New  Holland,  furnishes  a  number  of  very  curious  animals, 
which  are  not  found  on  the  Asiatic  continent.     Such  are  the 
herbivorous  bats,  and  the  Galeopithecus  or  flying  Maki.    The 
Galapago  islands,  only  a  few  hundred  miles  from  the  coast 
of  Peru,  have  a  fauna  exclusively  their  own,  among  which 
gigantic  land-tortoises  are  particularly  characteristic. 

SECTION    III 

CONCLUSIONS. 

441.  From  the  survey  we  have  thus  made  of  the  clistribu 
ti  jn  of  the -Animal  Kingdom,  it  follows  : 

1st.  Each  grand  division  of  the  globe  has  animals  which 
are  either  wholly  or  for  the  most  part  peculiar  to  it.  These 
groups  of  animal?  constitute  the  faunas  of  different  regions. 


208  GEOGRAPHICAL    DISTRIBUTION    OF    ANIMALS. 

2d.  The  diversity  of  faunas  is  not  in  proportion  to  the 
distan  :e  which  separates  them.  Very  similar  faunas  are 
found  at  great  distances  apart ;  as,  for  example,  the  fauna 
of  Europe  and  that  of  the  United  States,  which  yet  arc 
separated  by  a  wide  ocean.  Others,  on  the  contrary,  differ 
considerably,  though  at  comparatively  short  distances ;  as 
the  fauna  of  the  East  Indies  and  the  Sunda  Islands,  and  that 
of  New  Holland  ;  or  the  fauna  of  Labrador  and  that  of  New 
England. 

3d.  There  is  a  direct  relation  between  the  richness  of  a 
fauna  and  the  climate.  The  tropical  faunas  contain  a  much 
larger  number  of  more  perfect  animals  than' those  of  the 
temperate  and  polar  regions. 

4th.  There  is  a  no  less  striking  relation  between  the  fauna 
and  flora,  the  limit  of  the  former  being  oftentimes  deter- 
mined, so  far  as  terrestrial  animals  are  concerned,  by  the 
extent  of  the  latter. 

442.  Animals  are  endowed  with  instincts  and   faculties 
corresponding  to  the  physical  character  of  the  countries  they 
inhabit,  and  which  would  be  of  no  service  to  them  under 
other  circumstances.     The  monkey,  which  is  a  frugivorous 
animal,  is  organized  for  living  on  the  trees  from  which  he 
obtains  his  food.      The  reindeer,  on  the  contrary,  whose 
food  consists  of  lichens,  lives  in  cold  regions.     The  latter 
would  be  quite  out  of  place  in  the  torrid  zone,  and  the  mon- 
key would  perish  with  hunger  in  the  polar  regions.    Animals 
which  store  up  provisions  are  all  peculiar  to  temperate  or  coM 
climates.     Their  instincts  would  be  uncalled  for  in  tropical 
regions,  where  the  vegetation  presents  the  herbivora  with  an 
abundant  supply  of  food  at  all  times. 

443.  However  intimately  the  climate  of  a  country  seems  to 
be  allied  with  the  peculiar  character  of  its  fauna,  we  are  not 
to  conclude  that  the  one  is  the  consequence  of  the  other 
Tho  differences  which  are  observed  between  the  animals  of 


CONCLUSIONS.  209 

different  faunas  are  no  more  to  be  ascribed  to  the  influences 
of  climate,  than  their  organization  is  to  the  influence  of  the 
physical  forces  of  nature.  If  it  were  so,  we  should  necessa- 
rily find  all  animals  precisely  similar,  when  placed  under 
the  same  circumstances.  We  shall  find,  by  the  study  of  the 
different  groups  in  detail,  that  certain  species,  though  very 
nearly  alike,  are  nevertheless  distinct  in  two  different  faunas. 
Between  the  animals  of  the  temperate  zone  of  Europe,  and 
those  of  the  United  States,  there  is  similarity  but  not  iden- 
tity ;  and  the  particulars  in  which  they  differ,  though  ap- 
parently trifling,  are  yet  constant. 

444.  Fully  to  appreciate  the  value  of  these  differences,  it 
is  often  requisite  to  know  all  the  species  of  a  genus  or  of  a 
family.     It  is  not  uncommon  to  find,  upon  such  an  exam- 
ination, that  there  is  the  closest  resemblance  between  spe- 
cies that  dwell  far  apart  from  each  other,  while  species  of 
the  same  genus,  that  live  side  by  side,  are  widely  different. 
This  may  be  illustrated  by  a  single  example.     The  Menopo- 
ma,  Siren,  Amphiuma,  Axolotl,  and  the  Menobranchus,  are 
Batrachians  which  inhabit  the  rivers  and  lakes  of  the  United 
States  and   Mexico.      They  are   very  similar   in   external 
form,  yet  differ  in  the  fact  that  some  of  them  have  external 
gills  at  the  sides  of  the  head,  in  which  others  are  deficient ; 
that  some  have  five  legs,  while   others  are  only  provided 
with   two ;   and   also  in   having   either   two   or   four   legs. 
Hence  we  might  be  tempted  to  refer  them  to  different  types, 
did  we  not  know  intermediate  animals,  completing  the  series, 
namely,  the  Proteus  and  Megalobatrachus.     Now,  the  for- 
mer exists  only  in  the  subterranean  lakes  of  Austria,  and 
the  latter  in  Japan.     The  connection  in  this  case  is  conse- 
quently established  by  means  of  species  which  inhabit  con- 
tinents widely  distant  from  each  other. 

445.  Neither  the  distribution  of  animals,  therefore,  any 
more  than  their  organization,  can  be  the  effect  of  external 

18  • 


210  3EOGRAPHICAL    DIS~RIBUTION    OF    ANIMALS. 

influences.     We  must,  on  the  contrary,  see  in  it  the  reahza 
tion  of  a  plan  wisely  designed,  the  work  of  a  Supreme  Intel 
ligence  who  created,  at  the  beginning,  each  species  of  am« 
mal  at  the  place,  and  for  the  place,  which  it  inhabits.     To 
each  species  has  been  assigned  a  limit  which  it  has  no  dis- 
position to  overstep,  so  long  as  it  remains  in  a  wild  state. 
Only  those  animals  which  have  been  subjected  to  the  yoke 
of  man,  Dr  whose  subsistence  is  dependent  on  man's  social 
habits,  are  exceptions  to  this  rule. 

446.  As  the  human  race  has  extended  over  the  surface 
of  the  earth,  man  has  more  or  less  modified  the  animal  popu- 
lation of  different  regions,  either  by  exterminating  certain 
species,  or  by  introducing  others  with  which  he  desires  to  be 
more  intimately  associated  —  the  domestic  animals.     Thus 
the  dog  is  found  wherever  we  know  of  the  presence  of  man. 
The  horse,  originally  from  Asia,  was  introduced  into  Ameri- 
ca by  the   Spaniards;  where  it  has  thriven  so  well,  that  it 
is   found  wild,  in  innumerable  herds,  over  the  Pampas  of 
South    America,  and    the    prairies   of  the    West.     In    like 
manner,  the  domestic  ox   became  wild  in  South  America. 
Many  less  welcome  animals  have  followed  man  in  his  pere- 
grinations ;  as,  for  example,  the  rat  and  the  mouse,  as  well 
as  a  multitude  of  insects,  such  as  the  house-fly,  the  cock- 
roach, and  others  which  are  attached  to  certain  species  of 
plants,  as   the   white   butterfly,  the  Hessian  fly,  &c.     The 
honey-bee,  also,  has  been  imported  from  Europe. 

447.  Among  the  species  which  have  disappeared,  under 
the  influence  of  man,  we  may  mention  the  Dodo,  a  pecu- 
liar species    of  bird   which   once   inhabited   the   Mauritius, 
some  remains  of  which   are    preserved   in  the  British  and 
Ashmolean  Museums  ;  also  a  large  cetacean  of  the  north, 
(Rytina  Stelleri,)  formerly  inhabiting  the  coasts  of  Behring's 
Straits,  aid  which  has  not  been  seen  since  1768.     Ac-cord- 
ing to  al]  appearances,  we  must  also  count  among  these  the 


CONCLUSIONS.  211 

great  stag,  the  skeleton  and  horns  of  which  have  been  found 
buried  in  the  peat-bogs  of  Ireland.  There  are  also  manj 
species  of  animals  whose  numbers  are  daily  diminishing, 
and  whose  extinction  may  be  foreseen  ;  as  the  Canada  deer 
( Wapiti,)  the  Ibex  of  the  Alps,  the  Lammergeyer,  the 
bison,  the  beaver,  the  wild  turkey,  &c. 

448,  Other  causes  may  also  contribute  towards  dispersing 
animals  beyond  their  natural  limits.     Thus,  the  sea- weeds 
are  carried  about  by  marine  currents,  and  are  frequently 
met  with  far  from  shore,  thronged  with  little  crustaceans, 
which  are  in  this  manner  transported  to  great  distances  from 
vhe  place  of  their  birth.     The  drift  wood  which  the  Gulf 
Stream  floats  from  the  Gulf  of  Mexico  even  to  the  western 
shores  of  Europe,  is  frequently  perforated  by  the  larva?  of 
insects,  and  may,  probably,  serve  as  depositories  for  the  eggs 
of  fishes,  Crustacea,  and  mollusks.     It  is  possible,  also,  that 
aquatic  birds  may  contribute  in  some  measure  to  the  diffu- 
sion of  some  species  of  fishes  and  mollusks,  either  by  the 
eggs  becoming  attached  to  their  feet,  or  by  means  of  those 
which  they  evacuate   undigested,   after  having  transported 
them    to    considerable    distances.     Still,  all    these   circum- 
stances exercise  but  a  very  feeble  influence  upon  the  dis- 
tribution of  species  in  general ;  and  each  country,  none  the 
less,  preserves  its  peculiar  physiognomy,  so  far  as  its  animals 
are  concerned. 

449.  There  is  only  one  way  to  account  for  the  distribu- 
tion of  animals  as  we   find   them,  namely,  to  suppose  that 
they  are  autochthonal,  that  is  to  say,  that   they  originated 
like  plants,  on  the  soil  where  they  are  found.     In  order  to 
explain  the  particular  distribution  of  many  animals,  we  are 
even  led    to  admit  that   they  must   have    been   created    at 
several   points  o '  the  same   zone ;  an  inference  which  we 
must  make  from  The  distribution  of  aquatic  animals,  especial- 
ly that  of  Fishes.     If  we  examine  the  fishes  of  ihe  different 


212  GEOGRAPHICAL    DISTRIBUTION    OF    ANIMALS. 

rivers  of  the  United  States,  peculiar  species  will  be  fo  jnd  in 
each  basin,  associated  with  others  which  are  con.mon  to 
several  basins.  Thus,  the  Delaware  River  contains  species 
not  found  in  the  Hudson.  But,  on  the  other  hand,  the  pick- 
erel is  found  in  both.  Now,  if  all  animals  originated  at  one 
point,  and  from  a  single  stock,  the  pickerel  must  have  passed 
from  the  Delaware  to  the  Hudson,  or  vice  versa,  which  it 
could  only  have  done  by  passing  along  the  sea-shore,  or  by 
.eaping  over  large  spaces  of  terra  Jirma ;  that  is  to  say>  in 
both  cases  it  would  be  necessary  to  do  violence  to  its  organi- 
zation. Now,  such  a  supposition  is  in  direct  opposition  to 
the  immutability  of  the  laws  of  Nature. 

450.  We  shall  hereafter  see  that  the  same  laws  of  distri- 
bution are  not  limited  to  the  actual  creation  only,  but  that 
they  have  also    ruled    the   creations   of  former   geological 
epochs,  and  that  the  fossil  species  have  lived  and  died,  most 
of  them,  at  the  place  where  their  remains  are  found. 

451.  Even  Man,  although  a  cosmopolite,  is  subject,  in  a 
certain  sense,  to  this  law  of  limitation.     While  he  is  every 
where  the  one  identical  species,  yet  several  races,  marked 
by  certain  peculiarities  of  features,  are  recognized  ;   such  as 
the  Caucasian,  Mongolian,  and  African  races,  of  which  we 
are  hereafter  to  speak.     And  it  is  not  a  little  remarkable, 
that  the  abiding  places  of  these  several   races  correspond 
very    nearly    with  some   of    the    great   zoological    regions. 
Thus  we  have  a  northern  race,  comprising  the  Samoyedes 
in  Asia,  the  Laplanders  in  Europe,  and  the  Esquimaux  in 
America,   corresponding    to   the  arctic    fauna,  (400,)  and, 
like    it,    identical   on   the    three   continents,  having    for   its 
southern   limit   the  region  of  trees,  (422.)     In  Africa,  we 
have  the  Hottentot  and  Negro  races,  in  the  south  and  central 
portions  respectively,  while  the  people  of  northern  Africa 
are  a  lied  to  their  neighbors  in  Europe;  just  as  we  have 
seen  to  be  the  case  with  the  zoological  fauna  in  general 


CONCLUSIONS  213 

(403.)     The  inhabitants  of  New  Holland,  like   its  animals 
are  the  most  grotesque  and  uncouth  of  all  races,  (433.) 

452.  The  same  parallelism  holds  good  elsewhere,  though 
not  always  in  so  remarkable  a  degree.  In  America,  espe- 
cially, while  the  aboriginal  race  is  as  well  distinguished  from 
other  races  as  is  its  flora,  the  minor  divisions  are  not  so 
decided.  Indeed,  the  facilities,  or  we  might  sometimes 
rather  say  necessities,  arising  from  the  varied  supplies  of 
animal  and  vegetable  food  in  the  several  regions,  might  be 
expected  to  involve,  with  his  corresponding  customs  and 
modes  of  life,  a  difference  in  the  physical  constitution  of 
man,  which  would  contribute  to  augment  any  primeval  dif- 
ferences. •  It  could  not  indeed  be  expected,  that  a  people 
constantly  subjected  to  cold,  like  the  people  of  the  North, 
and  living  almost  exclusively  on  fish,  which  is  not  to  be 
obtained  without  great  toil  and  peril,  should  present  the  same 
characteristics,  either  bodily  or  menta  ,  as. those  who  idly 
regale  on  the  spontane  >us  bounties  of  tropical  vegetation 


CHAPTER    FOURTEENTH 

GEOLOGICAL    SUCCESSION    OF    ANIMALS;     OR,    THEIR 
DISTRIBUTION   IN   TIME. 

SECTION  L 

STRUCTURE     OF     THE     EARTH'S     CRUST, 

453.  THE  records  of  the  Bible,  as  well  as  human  tra- 
dition, teach  us  that  man  and  the  animals  associated  with 
him  were  created  by  the  word  of  God ;  "  the  Lord  made 
heaven  and   earth,  the  sea,  and  all  that  in  them  is;"  and 
this  truth  is  confirmed  by  the  revelations  of  science,  which 
unequivocally  indicate   the   direct   interventions  of  creative 
power. 

454.  But  man  and  the  animals  which  now  surround  him 
are  not  the  only  kinds  which  have  had  a  being.     The  sur- 
face of  our  planet,  anterior  to  their  appearance,  was  not  a 
desert.     Tnere  are,  scattered  through  the  crust  of  the  earth, 
numerous  animal  and  vegetable  remains,  which  show  that 
the  earth   had  been  repeatedly  supplied  with,  and  long  in- 
habited by,  animals  and  plants  altogether  different  from  those 
now  living. 

455.  In  general,  their  hard  parts  are  the  only  relics  of 
them  which  have  been  preserved,  such  as  the  skeleton  and 
teeth  of  Vertebrates  ;  the  shells  of  the  Mollusks  and  Radiata ; 
the  shields  of  the  Crustaceans,  and  sometimes  the  wing-cases 
of  Insects.     Most   frequently  they  have  lost  their  original 


STETTCTURE    OF    THE    EARTHS    CRUST.  215 

chemical  composition,  and  are  changed  into  stone ;  and 
hence  the  name  of  petrifactions  or  fossils,  under  which  lat- 
ter term  are  comprehended  all  the  organized  oodles  of 
former  epochs,  obtained  from  the  earth's  crust.  Others  have 
entirely  disappeared,  leaving  only  their  forms  ai  d  sculpture 
impressed  upon  the  rocks. 

456.  The  study  of  these  remains  and  of  their  position  in 
the  rocks  constitutes  PALEONTOLOGY  ;  one  of  the  most  essen- 
tial branches  of  Zoology.     Their  geological  distribution,  or 
the  order  of  their  successive  appearance,  namely,  the  distri- 
bution  of  animals  in  time,  is  of  no  less  importance  than  the 
geographical  distribution  of  living  animals,  their  distribution 
in  space,  of  which  we  have  treated  in  the  preceding  chapter. 
To  obtain  an  idea  of  the  successive  creations,  and  of  the  stu- 
pendous length  of  time  they  have  required,  it  is  necessary  to 
sketch  the  principal  outlines  of  Geology. 

457.  The  rocks*  which  compose  the  crust  of  our  globe 
are  of  two  kinds  : 

1.  The  Massive  Rocks,  called  also  Plutonic  or  Igneous 
Rocks,  which  lie  beneath  all  the  others,  or  have  sometimes 
been  forced  up  through   them,  from   beneath.     They  were 
once  in  a  melted  state,  like  the  lava  of  the  present  epoch, 
and  on  cooling  at  the  surface  formed  the  original  crust  of  the 
globe,  the  granite,  and  later  porphyry,  basalt,  &c. 

2.  The  Sedimentary  or  Stratified  Rocks,  called  also  Nep- 
tunic  Rocks,  which  have  been  deposited  in  water,  in  the  same 
manner  as  modern  seas  and  lakes  deposit  sand  and  mud  on 
their  shores,  or  at  the  bottom. 

458.  These  sediments  have  been  derived  partly  from  the 
disintegration  of  the  older  rocks,  and  partly  from  the  decay 
of  plants  and  animals.     The  materials  being  disposed  in 


*  Rocks,  in  a  geological  sense,  include  all  the  materials  of  the  earth. 
the  loose  soil  and  gravel,  as  well  as  the  firm  rock. 


216  GEOLOGICAL    SUCCESSION    OF    ANIMALS. 

layers  or  strata,  have  become,  as  they  hardened,  limestones, 
slates,  marls,  or  grits,  according  to  their  chemical  and  me- 
chanical composition,  and  contain  the  remains  of  the  animals 
and  plants  \vhich  were  scattered  through  the  waters.* 

459.  The  different  strata,  when  undisturbed,  are  arranged 
one  above  the  other  in  a  horizontal  manner,  like  the  leaves 
of  a  book,  the  lowest  being  the  oldest.     In  consequence  of 
the  commotions  which  the  crust  of  the  globe  has  undergone, 
the  strata  have  been  ruptured,  and  many  points  of  the  surface 
have  been  elevated  to  great  heights,  in  the  form  of  moun- 
tains ;  and  hence  it  is  that  fossils  are  sometimes  found  at  the 
summit  of  the  highest  mountains,  though  the  rocks  contain- 
ing them  were  originally  formed  at  the  bottom  of  the  sea. 
But  even  when  folded,  or  partly  broken,  their  relative  age 
may  still  be  determined  by  an  examination  of  the  ends  of 
the  upturned  strata,  where  they  appear  or  crop  out  in  suc- 
cession, at  the  surface,  or  on  the  slopes  of  mountains,  as  seen 
in  the  diagram,  (Fig.  154.) 

460.  The  sedimentary  rocks  are  the  only  ones  which  have 
been  found  to  contain  animal  and  vegetable  remains.     These 
are  found  imbedded  in  the  rock,  just  as  we  should  find  them 
in  the  mud  now  deposited  at  the  bottom  of  the  sea,  if  laid 
dry.     The  strata  containing  fossils  are  numerous.     The  com- 
parison and  detailed  study  of  them  belongs  to  Geology,  of 

*  Underneath  the  deepest  strata  containing  fossils,  between  these  and 
the  Plutonic  rocks,  are  generally  found  very  extensive  layers  of  slates 
without  fossils,  (gneiss,  mica-slate,  talcose-slate,)  though  stratified,  and 
known  to  the  geologist  under  the  name  of  Metamorphic  Rocks,  (Fig.  154, 
AT,)  being  probably  sedimentary  rocks,  which  have  undergone  consider- 
able changes.  The  Plutonic  rocks,  as  well  as  the  metamorphic  rocks, 
are  not  always  confined  to  the  lower  levels,  but  they  are  often  seen  rising 
to  considerable  heights,  and  forming  many  of  the  loftiest  peaks  of  the 
globe.  The  former  also  penetrate,  in  many  cases,  like  veins,  through  the 
whole  mass  of  the  stratified  and  metamorphic  layers,  and  expand  at  the 
surface ;  as  is  the  case  with  the  trap  dykes,  and  as  lava  streams  actually 
Jo  at  the  present  era,  (Fig.  154,  T.  L.) 


STRUCTURE  OF  THE  EARTH'S  CRUST. 


211 


w.iich  Paleontology  forms  an  essential  part.  A  group  of 
strata  extending  over  a  certain  geographical  extent,  all  of 
which  contain  some  fossils  in  common,  no  matter  what  may 
be  the  chemical  character  of  the  rock,  whether  it  be  lime- 
stone, sand,  or  clay,  is  termed  a  geological  Formation.  Thus, 
the  coal  beds,  with  the  intervening  slates  and  grits,  and  the 
masses  of  limestone,  between  which  they  often  lie,  constitute 
but  one  formation  —  the  carboniferous  formation. 

461.  Among  the  stratified  rocks  we  distinguish  ten  prin- 
cipal Formations,  each  of  which  indicates  an  entirely  new 
era  in  the  earth's  history  ;  while  each  of  the  layers  which 
compose  a  formation  indicates  but  some  partial  revolution. 
Proceeding  from  below  upwards^  they  are  as  follows,  as 
indicated  in  the  cut,  and  also  in  the  lower  diagram  on  the 
Frontispiece. 


Fig.  15*. 

l*t  The  Lower  Silurian.  This  is  a  most  extensive  for- 
mation, no  less  than  eight  stages  of  which  have  been  made 
out  by  Geologists  in  North  America,  composed  of  various 
limestones  and  sandstones.* 

*  1.  Potsdam  Sandstone ;  2.  Calciferous  Sandstone ;  3.  Chazy  Lime 
stone  ;  4.  Bird's-eye  Limestone ;  5.  Black  River'Limestone ;  6.  Trenton 
Limestone ;  7-  Utica  Slate ;  8.  Hudson  River  Group  ;  being  all  found  in 
the  western  parts  of  the  United  States. 

19 


218  GEOLOGICAL    SUCCESSION    Ol    ANIMALS. 

2d.  The  Upper  Silurian.  It  is  also  a  very  extensive  for- 
mation, since  about  ten  stages  of  it  are  foui-d  in  the  State  of 
New  York.* 

3d.  The  Devonian,  including  in  North  America  no  less 
than  eleven  stages.t  It  occurs  also  in  Russia  and  Scotland, 
where  it  was  first  made  out  as  a  peculiar  formation. 

4th.  The  Carboniferous  Formation,  consisting  of  three 
grand  divisions. J 

5th.  The  Trias,  or  Saliferous  Formation,  which,  contain- 
ing the  richest  deposits  of  Salt  on  the  continent  of  Europe, 
comprises  three  stages,^  to  one  of  which  the  Sandstone  of 
the  Connecticut  valley  belongs. 

6th.  The  Oolitic  Formation,  only  faint  traces  of  which 
exist  on  the  continent  of  America.  It  comprises  at  least  four 
distinct  stages.  || 

7th.  The  Cretaceous,  or  Chalk  Formation,  of  which  three 
principal  stages  have  been  recognized,  two  of  which  are 
feebl)  represented  in  this  country,  in  the  Southern  and  Mid- 
dle States. 

8th.  The  Lower  Tertiary,  or  Eocene,  very  abundant  in  the 
Southern .  States  of  the  Union,  and  to  which  belong  the 
coarse  limestone  of  Paris,  and  the  London  clay  in  England. 

*  1.  Onei da  Conglomerate;  2.  Medina  Sandstone;  3.  Clinton  Group; 
4.  Niagara  Group ;  5.  Onondaga  Salt  Group ;  6.  Wuter  Limestone ; 
7.  Pentamerus  Limestone ;  8.  Delthyris  Shaly  Limestone ;  9.  EncrinaJ 
Limestone ;  10.  Upper  Pentamerus  Limestone. 

•f  1.  Oriskany  Sandstone;  2.  Cauda-Galli  Grit;  3.  Onondaga  Lime- 
stone; 4.  Corniferous  Limestone;  5.  Marcellus  Shale;  6.  Hamilton 
Group ;  7-  Tully  Limestone ;  8.  Genesee  Slate ;  9.  Portage  Group ; 
10.  Chemung  Group  ;  11.  Old  Red  Sandstone. 

J  1.  The  Permian,  extensively  developed  in  Russia,  especially  in  the 
government  of  Perm  ;  2.  The  coal  measures,  containing  the  rich  deposits 
of  coal  in  the  Old  and  New  World ;  3.  The  Magnesian  Limestone  of 
England. 

§  1.  New  Red  Sandstone ;  2.  Muschelkalk ;  3.  Keuper. 

||  1.  The  Lias ;  2.  The  Lower  Oolite ;  3.  The  Middle  Oolite ;  4  The 
Upper  Oolite 


bTRUCTURE  OF  THE  EARTH'S  CRUST.         219 


9tli.  The  Upper  Tertiary,  or  Miocene  and 
found  also  in  the  United  States,  as  far  north  as  Martha  s 
Vineyard  and  Nantucket,  and  very  extensive  in  Southerr. 
Europe,  as  well  as  in  South  America. 

10th.  The  Drift,  forming  the  most  superficial  deposits, 
and  extending  over  a  large  portion  of  the  northern  countries 
in  both  hemispheres. 

We  have  thus  more  than  forty  distinct  layers  already 
made  out,  each  of  which  marks  a  distinct  epoch  in  the  earth's 
history,  indicating  a  more  or  less  extensive  and  important 
change  in  the  condition  of  its  surface. 

462.  All  the  formations  are  not  every  where  found,  or  are 
not  developed  to  the  same  extent,  in  all  places.  So  it  is 
with  the  several  strata  of  which  they  are  composed.  In 
other  words,  the  layers  of  the  earth's  crust  are  not  continuous 
throughout,  like  the  coats  of  an  onion*  There  is  no  place  on 
the  globe  where,  if  it  were  possible  to  bore  down  to  its 
centre,  all  the  strata  would  be  found.  It  is  easy  to  under- 
stand how  this  must  be  so.  Since  irregularities  in  the 
distribution  of  water  upon  the  solid  crust  have,  necessarily, 
always  existed  to  a  certain  extent,  portions  of  the  earth's 
surface  must  have  been  left  dry  at  every  epoch  of  its 
history,  gradually  forming  large  islands  and  continents,  as 
the  changes  were  multiplied.  And  since  the  rocks  were 
formed  by  the  subsidence  of  sediment  in  water,  no  rocks 
would  be  formed  except  in  regions  covered  by  water  ;  they 
would  be  thickest  at  the  parts  where  most  sediment  was 
deposited,  and  gradually  thin  out  towards  their  circumference. 
We  may  therefore  infer,  that  all  those  portions  of  the  earth's 
surface  which  are  destitute  of  a  certain  formation  were  dry 
land,  during  that  epoch  of  the  earth's  history  to  which  such 
formation  relates,  excepting,  indeed,  where  the  rocks  have 
been  subsequently  removed  by  the  denuding  action  of  water 
or  other  causes. 


(EC LOGICAL    SUCCESSION    OF   ANIMALS 

463.  Each  formation  represents  an  immense  period    of 
time,  during  which  the  earth   was   inhabited  by  successive 
races  of  animals  and  plants,  whose  remains  are  often  found 
in  their  natural  position,  in  the  places  where  they  lived  and 
died,  not  scattered  at  random,  though  sometimes  mingled  to- 
gether by  currents  of  water,  or  other  influences,  subsequent 
to  the  time  of  their  interment.     From  the  manner  in  which 
the  remains  of  various  species  are  found  associated  in  the 
rock,  it  is  easy  to  determine  whether  the  animals  to  which 
these  remains  belonged  lived  in  the  water,  or  on  land,  on  the 
beach  or  in  the  depths  of  the  ocean,  in  a  warm  or  in  a  cold 
climate.     They  will  be  found  associated   in  just  the  same 
way  as  animals  are  that  live  under  similar  influences  at  the 
present  day. 

464.  In  most  geological  formations,  the  number  of  spe- 
cies of  animals  and  plants  found  in  any  locality  of  given 
extent,  is  not  below  that  of  the  species  now  living  in  an 
area  of  equal  extent  and  of  a  similar  character;  for  though, 
in  some  deposits,  the  variety  of  the  animals  contained  may 
be  less,  in  others  it  is  greater  than  that  on  the  present  surface. 
Thus,  the  coarse  limestone  in  the  neighborhood  of  Paris, 
which  is  only  one   stage  of  the  lower  tertiary,  contains  not 
less  than  1200  species  of  shells  ;  whereas  the  species  now 
living  in  the  Mediterranean  do  not  amount  to  half  that  num- 
ber.     Similar  relations  may  be   pointed    out   in  America. 
Mr.  Hall,  one  of  the  geologists  of  the  New  York  Survey,  has 
described,  from  the  Trenton  limestone,  (one  of  the  ten  stages 
of  the  lower  Silurian,)  170  species  of  shells,  a  number  almost 
equal  tD  that  of  all  the  species  found  now  living  on  the  coast 
of  Massachusetts. 

465.  Nor  was  the   number  of  individuals  less   than   at 
present.     Whole  rocks  are  entirely  formed   of  animal  re- 
mains, particularly  of  corals  and  shells.     So,  also,  coal  is 
compos  3d  of  the  remains  of  plants.     If  we  consider  the  slow 


OF    NATURE.  221 

ness  with  wl  ich  corals  and  shells  are  formed,  it  will  give  us 
some  fa  nt  notion  of  the  vast  series  of  ages  that  must  have 
elapsed  in  order  to  allow  the  formation  of  those  rocks,  and 
their  regular  deposition,  under  the  water,  to  so  great  a  thick- 
ness. If,  as  all  things  combine  to  prove,  this  deposition  took 
place  in  a  slow  and  gradual  manner  in  each  formation,  we 
must  conclude,  that  the  successive  species  of  animals  found 
In  them  followed  each  other  at  long  intervals,  and  are  not  the 
work  of  a  single  epoch. 

466.  It  was  once  believed  that  animals  were  successively 
created  in  the  order  of  their  relative  perfection ;  so  that  the 
most  ancient  formations  contained  only  animals  of  the  low- 
est grade,  such  as  the  Polyps,  the  Echinoderms,  to  which 
succeeded  the  Mollusks,  then  the  Articulated  Animals,  and, 
last  of  all,  the  Vertebrates.  This  theory,  however,  is  now 
untenable  ;  since  fossils  belonging  to  each  of  the  four  depart 
ments  have  been  found  in  the  fossiliferous  deposits  of  every 
age.  Indeed,  we  shall  see  that  even  in  the  lower  Silurian 
formation  there  exist  not  only  Polyps  and  other  Radiata,  but 
also  numerous  Mollusks,  Trilobites,  (belonging  to  the  Articu- 
lata,)  and  even  Fishes. 


SECTION   II. 

AGES    OF    NATURE. 

467.  Each  formation,  as  has  been  before  stated,  (460,) 
contains  remains  peculiar  to  itself,  which  do  not  extend  into 
the  neighboring  deposits  above  or  below  it.  •Still  there  is  u 
connection  between  the  different  formations,  more  strong  in 
proportion  to  their  proximity  to  each  other.  Thus,  the  ani- 
mal remains  of  the  Chalk,  while  they  differ  from  those  of  all 
other  formations,  are,  nevertheless,  much  more  nearly  related 
19* 


222  GEOLOGICAL    SUCCESS  ON    OF    ANIMALS 

to  those  of  the  Oolitic  formation,  which  immediately  precedes, 
than  to  those  of  the  carboniferous  formation,  which  is  much 
more  ancient;  and,  in  the  same  manner,  the  fossils  of  the 
carboniferous  group  approach  more  nearly  to  those  of  the 
Silurian  formation  than  to  those  of  the  Tertiary. 

468.  These  relations  could  not  escape  the  observation  of 
naturalists,  and  indeed  they  are  of  great  importance  for  the 
true  understanding  of  the  development  of  life  at  the  surface 
of  our  earth.     And,  as  in  the  history  of  man,  several  grand 
periods  have  been  established,  under  the   name  of  Ages, 
marked  by  peculiarities  in  his  social  and  intellectual  condi- 
tion, and  illustrated  by  contemporaneous  monuments,  so,  in 
the  history  of  the  earth,  also,  are  distinguished  several  great 
periods,  which  may  be  designated  as  the  various  Ages  of 
Nature,  illustrated,  in  like  manner,  by  their  monuments,  the 
fossil  remains,  which,  by  certain  general,  traits  stamped  upon 
them,  clearly  indicate  the  eras  to  which  they  belong. 

469.  We  distinguish  four  Ages  of  Nature,  corresponding 
to  the  great  geological  divisions,  namely : 

1st.  The  Primary  or  Palceozoic  Age,  comprising  the  lower 
Silurian,  the  upper  Silurian,  and  the  Devonian.  During  this 
age  there  were  no  air-breathing  animals.  The  fishes  were 
the  masters  of  creation.  We  may  therefore  call  it  the  Reign 
of  Fishes. 

2d.  The  Secondary  Age,  comprising  the  carboniferous  for- 
mation, the  Trias,  the  Oolitic,  and  the  Cretaceous  formations. 
This  is  the  epoch  in  which  air-breathing  animals  first  appear. 
Reptiles  predominate  over  the  other  classes,  and  we  may 
therefore  call  it  the  Reign  of  Reptiles. 

3d.  The  Tertiary  Age,  comprising  the  tertiary  formations. 
During  this  age,  terrestrial  mammals,  of  great  size,  abound. 
This  is  the  Reign  of  Mammals. 

4th.  The  Modern  Age,  characterized  by  the  appearance 
of  the  most  perfect  of  all  created  beings.  This  is  the  Reign 
of  Man. 


AGES    OF    NATURE. 


583 


Let  us  review  each  of  these  four  Ages  of  Nature,  with 
reference  to  the  diagram  at  the  beginning  of  the  volume. 

470.  THE  PALAEOZOIC  AGE.  Reign  of  Fishes.  —  The 
palaeozoic  fauna,  being  the  mos*  remote  from  the  present 
epoch,  presents  the  least  resemblance  to  the  animals  now 
existing,  as  will  easily  be  perceived  by  a  glance  at  the  fol- 


Fig.  155. 

lowing  sketches,  (Fig.  155.)  In  no  other  case  do  we  mees 
with  animals  of  such  extraordinary  shapes,  as  in  the  strata 
of  the  Palaeozoic  age. 

471.  We  have  already  stated  (466)  that  there  are  found, 
in  each  formation  of  the  primary  age,  animal  remains  of  all 
the  four  great  departments,  namely,  vertebrates,  articulata, 
mollusks,  and  radiata.  We  have  now  to  examine  to  what 
peculiar  classes  and  farrilies  of  each  department  these  re- 
mal'is  belong,  with  avieu  o  ascertain  if  any  relation  between 


224  GEOLOGICAL    SUCCESSION    OF    ANIMALS. 

the  structure  of  an  animal,  and  the  epoch  of  its  first  appear 
arice  on  the  earth's  surface,  may  be  traced. 

472.  As  a  general  result  of  the  inquiries  hitherto  made, 
it  may  be  stated  that  the  palaeozoic  animals  belong,  for  the 
most  part,  to  the   lower  divisions  of  the  different  classes. 
Thus,  of  the  class  of  Echinoderms,  we   find   scarcely  any 
but  Crinoids,  which  are  the  least  perfect  of  the  class.     We 
have  represented,  in  the  above  sketches,  several  of  the  most 
curious  forms,*  as  well  as  of  the  Polyps,  of  which  there  are 
some  quite  peculiar  types  from  the  Trenton  limestone,  and 
from  the  Black  River  limestone. 

473.  Of  the   Mollusks,  the  bivalves  or  Acephab  are  nu- 
merous, but,  for  the  most  part,  they  belong  to  the  Brachiopo- 
da,  that  is  to  say,  to  the  lowest  division  of  the  class,  including 
mollusks  with  unequal  valves,  having  peculiar  appendages 
in  the  interior.     The  Leptcena  alternata,  (£,)  which  is  found 
very  abundantly  in  the  Trenton  limestone,  is  one  of  these 
shells.    The  only  fossils  yet  found  in  the  Potsdam  sandstone, 
the  oldest  of  all  fossiliferous  deposits,  belong,  also,  to  this 
family,  (Lingula  prima,  a.)     Besides  this,   there  are   also 
found  some   bivalves  of  a  less  uncommon  shape,  (Avicula 
decussata,  e.) 

474.  The  Gasteropods  are  less  abundant ;  some  of  them 
are  of  a  peculiar  shape  and  structure,  (Bucania  expansa,f; 
Euomphalus  hemisphericus,  c.)     Those  more  similar  to  our 
common  marine  snails  have  all   an  entire  aperture  ;  those 
with  a  canal  being  of  a  more  recent  epoch. 

475.  Of  the  Cephalopods  we  find   some  genera  not  less 
curious,  part  of  which  disappear  in  the  succeeding  epochs ; 


*  (i)Cyathocrinus  ornatissimus,  Hall ;  (J )  Melocrinus  Amphora,  Goldf. ; 
(A)  Cariocrinus  ornatus,  Say;  (I)  Columnaria  alveolata;  (m)  Cyatho- 
phyllum  qur.d*igeminum,  Goldf. ;  (nt  6)  Caninia  flexuosa ;  (p)  Chcetetes 
lycopwdon. 


AGES    OF    NATURE. 


225 


suci,  in  particular,  as  those  of  the  straigh.,  chambered  shells 
called  Orthoceratites,  some  of  which  are  twelve  feet  in  length, 
(Orthoceras  fusiformc,  g.)  There  are  also  found  some  of  a 
coiled  shape,  like  the  Ammonites  of  the  secondary  age,  but 
having  less  complicated  partitions, (Trocholites ammonius,d.) 
The  true  cuttle-fishes,  which  are  the  highest  of  the  class, 
are  not  yet  found.  On  the  contrary,  the  Bryozoa,  which 
have  long  been  considered  as  polyps,  but  which,  according 
to  all  appearances,  are  mollusks  of  a  very  low  order,  are 
very  numerous  in  this  epoch. 

476.  The  Articulata  of  the  Paleozoic  age  are  mostly 
Trilobites,  animals  which  evidently  belong  to  the  lower 
order  of  the  Crustaceans,  (Fig.  156.)  There  is  an  incom- 
pleteness and  want  of  development,  in  the  form  of  their 
body,  that  strongly  reminds  us  of  the  embryo  among  the 
crabs.  A  great  many  genera  have  already  been  discovered. 


Fig.  156. 


We  may  consider  as  belonging  to  the  more  extraordinary 
the  forms  here  represented,  (Harpes,  a ;  Arges,  b ;  Bron* 
tes,  c ;  and  Platynotus,  d  ;)  the  latter,  as  well  as  the  Isotelus 
the  largest  of  all,  being  peculiar  to  the  Paleozoic  deposit  of 
this  country.  Some  others  seem  more  allied  to  the  crusta- 
ceans  of  the  following  ages,  but  are  nevertheless  of  a  very 
extraordinary  form,  as  Eurypterus  remipes,  (e.)  There  are 
a. so  found,  in  the  Devonian,  some  very  large  Entomostraca. 
The  class  of  WDrms  is  represented  only  by  a  few  Serpulse, 


226 


GEOLOGICAL    SUCCESSION     OF   ANIMALS. 


which  are  marine  worms,  surrounded  by  a  solid  sheath.    The 
class  DI  Insects  is  entirely  wanting. 

477.  The    inferiority  of  the  earliest  inhabitants  of  our 
earth  appears  most  striking  among  the  Vertebrates.     There 
are  as  yet  neither  reptiles,  birds,  nor  mammals.    The  fishes, 
as  we  have  said,  are  the  sole  representatives  of  this  division 
of  animals. 

478.  But  the   fishes  of  that  early  period  were  not  like 
ours.     Some  of  them  had  the  most  extraordinary  forms,  so 
that  they  have  been  often  mistaken  for  quite  different  ani- 
mals ;  for  example,  the  Pterichthys,  (a,)  with  its  two  wing- 


Fig.  157. 

like  appendages,  and  also  the  Coccosteus  (b)  of  the  samo 
deposit,  with  its  large  plates  covering  the  head  and  the  ante- 
rior part  of  the  body.  There  are  also  found  remains  of 
shark's  spines,  (e,)  as  well  as  palatal  bones,  (rf,)  the  latter  of  a 
very  peculiar  kind.  Even  those  fishes  which  have  a  more 
regular  shape,  as  the  Dipterus,  (c,)  have  not  horny  scales 
like  our  common  fishes,  but  are  protected  by  a  coat  of  bony 
plates,  covered  with  enamel,  like  the  gar-pikes  of  the 
American  rivers.  Moreover,  they  all  exlybit  certain  char- 
acteristic features,  which  are  very  interesting  in  a  physio- 
logical point  o/  view.  They  all  have  a  broad  head,  and  a 
tail  terminafing  in  two  unequal  lobes.  What  is  still  more 
curious,  the  best  preserved  specimens  show  no  indications 


AGES    OF    NATURE.  227 

of  the  bodies  of  vertebrse,  but  merely  of  their  spinous  pro- 
cesses ;  from  which  it  must  be  inferred  that  the  body  of  the 
vertebra  was  cartilaginous,  as  it  is  in  our  Sturgeons. 

479.  Recurring  to  what  has  been  stated  on  that  point,  in 
Chapter  Twelfth,  we  thence  conclude,  that  these   ancient 
fishes  were  not  so  fully  developed  as  most  of  our  fishes, 
being,  like  the  Sturgeon,  arrested,  as  it  were,  in  their  devel- 
opment ;  since  we  have  shown  that  the  Sturgeon,  in  its  or- 
ganization, agrees,  in  many  respects,  with  the  Cod  or  Salmon 
at  an  early  age. 

480.  Finally,  there  was,  during  the  Paleozoic  age,  but 
liitle  variety  among  the  animals  of  the  different  regions  of 
the  globe ;  and  this  may  be  readily  explained  by  the  pecu- 
liar configuration  of  the  earth  at  that  epoch.     Great  moun- 
tains did  not  then  exist ;  there  were  neither  lofty  elevations 
nor  deep  depressions.     The  sea  covered  the  greater  part,  if 
not  the  whole,  of  the  surface  of  the  globe ;  and  the  animals 
which  then  existed,  and  whose  remains  have  been  preserved, 
were  all,  without  exception,  aquatic  animals,  breathing  by 
gills.     This  wide  distribution  of  the  waters  impressed  a  very 
uniform  character  upon  the  whole  Animal  Kingdom.     Be- 
tween the  different  zones  and  continents,  no  such  strange 
contrasts  of  the  different  types  existed  as  at,  the   present 
epoch.     The  same  genera,  and  often  the  same  species,  were 
found  in  the  seas  of  America,  Europe,  Asia,  Africa,  and 
New    Holland  ;    from    which    we    must   conclude   that  the 
climate  was  much  more  uniform  than  at  the  present  day. 
Among  the  aquatic  population,  no  sound  was  heard.     All 
creation  w^s  then  silent. 

481.  THE  SECONDARY  AGE.  Reign  of  Reptiles. — The 
Secondary  age  displays  a  greater  variety  of  animals  as  well 
as  plants.  The  fantastic  forms  of  the  Palseozoic  age  disap« 
pear,  and  in  their  place  we  see  a  greater  symmetry  of  shape. 
The  advance  is  particularly  marked  in  the  series  of  verte- 


228  GLOLOGICAL    SUCCESSION    OF    ANIMALS. 

brates.  Fishes  are  no  longer  the  sole  representatives  ol 
that  department.  Reptiles,  Birds,  and  Mammals  successive 
ly  make  their  appearance,  but  Reptiles  are  preponderant 
particularly  in  the  oolitic  formation ;  on  which  account  we 
have  called  this  the  Reign  of  Reptiles. 

482.  The  carboniferous  formation  is  the  most  ancient  of 
the  Secondary  age.     Its  fauna  bears,  in  various  respects,  a 
close  analogy  to  that  of  the  Palaeozoic  epoch,  especially  in 
its  Trilobites  and  Mollusks.*     Besides  these,  we  meet  here 
with  the  first  air-breathing  animals,  which   are   Insects  and 
Scorpions.     At  the  same  time,  land-plants  first  make  their 
appearance,  namely,  ferns   of  great  size,  club-mosses,  and 
other  fossil  plants.    This  corroborates  what  has  been  already 
said   concerning   the   intimate    connection    that   exists,  and 
from  all  times  has  existed,  between  animals  and  the  land- 
plants,  (399.)     The  class  of  Crustaceans  has  also  improved 
during  the  epoch  of  the  coal.     It  is  no  longer  composed  ex- 
clusively of  Trilobites,  but  the  type  of  horse-shoe  crabs  also 
appears,  with  other  gigantic  forms.     Some  of  the  Mollusks 
seem  also  to  approach  those  of  the  Oolitic  period,  particularly 
the  Bivalves. 

483.  In  the  Trias  period,  which  immediately  succeeds  the 
Carboniferous,  the  fauna  of  the  Secondary  age  acquires  its 
definitive  character ;  here  the  Reptiles  first  appear.    They  are 
huge  Crocodilian  animals,  belonging  to  a  peculiar  order,  the 
Rhizodonts,  (Protosaurus,  Notosaurus,  and  Labyrinthodon.) 
The  well-known  discoveries  of  Professor  Hitchcock,  in  the 
red  sandstone  of  the  Connecticut,  have  made  us  acquainted 

*  This  circumstance,  in  connection  with  the  absence  of  Reptiles,  has 
caused  the  coal-measures  to  be  generally  referred  to  the  Palaeozoic  epoch. 
But  there  are  other  reasons  which  induce  us  to  unite  the  carboniferous 
pa;iod  with  the  secondary  age,  especially  when  considering  that  here  the 
land  animals  first  appear,  whereas,  in  the  Palaeozoic  age,  there  are  only 
marine  animals,  breathing  by  gills  ;  and,  also,  that  a  luxuriant  terrestrial 
vegetation  Avas  developed  at  that  epoch. 


AGES  OF  NATURE. 


229 


with  a  grca  number  of  birds'  tracks  (Fig.  158,  a,  fc)  belong- 
ing to  this  epoch,  for  the  most  part  indicating  birds  of  gigan- 
tic size.  These  impressions,  which  he  has  designated  under 
the  name  of  Ornithichnites,  are  some  of  them  eighteen  inches 


a  Fig.  158. 

in  length,  and  five  feet  apart,  far  exceeding  in  size  the  tiacks 
of  the  largest  ostrich.  Other  tracks,  of  a  very  peculiar  shape, 
have  been  found  in  the  red  sandstone  of  Germany,  and  in 
Pennsylvania.  They  were  probably  made  by  Reptiles  which 
have  been  called  Cheirotherium,  from  the  resemblance  of  the 
track  to  a  hand,  (c.)  The  Mollusks,  Articulates,  and  Raaiates 
of  this  period,  approach  to  the  fauna  of  the  succeeding  period. 
484.  The  fauna  of  the  Oolitic  formation  is  remarkable  for 
the  great  number  of  gigantic  Reptiles  which  it  contains.  In 


Fig.  .159. 


this  formation  we  find  those  enormous  Amphibia,  known 
under  the  names  Ichthyosaurus,  Plesiosaurus,  Megdlosaurus* 
and  Iguanodon.  The  first,  in  particular,  the  Ichthyosaurus, 
(Fig.  159,  a,)  greatly  abounded  on  the  coast  of  the  continents 
of  that  period,  and  their  skeletons  are  so  well  preserved,  that 
we  are  enabled  to  study  even  the  minutest  details  of  their 
structure,  which  differs  essentially  from  that  of  the  Reptiles 
of  the  present  day.  In  some  respects  they  form  an  inter- 
mediate link  between  the  Fishes  and  Mammals,  and  may  be 
considered  as  the  prototypes  of  the  Whales,  having,  like 
20 


230  GEOLOGICAL    SUCCESS- ON    OF    ANIMALS. 

then),  limbs  in  the  form  of  oars.  The  Plesiosaurus  (b) 

agrees,  in  many  respects,  with 
the  Ichthyosaurus,  in  its  struc- 
ture, but  is  easily  distinguished 
by  its  long  neck,  which  resem- 
bles somewhat  the  neck  of 
some  of  our  birds.  A  still 
more  extraordinary  Reptile  is 
Fig.  160.  the  Pterodactylus,  (Fig.  160,) 

with  its  long  fingers,  like  those  of  a  bat,  and  which  is  thought 

to  have  been  capable  of  flying. 

485.  It  is  also  in  the  upper  stages  of  this  formation  that 
we  first  meet  with  Tortoises.     Here  also  we  find  impressions 
of  several  families  of  insects,  (Libellulce,  Coleoptera,  Ichneu- 
mons, fyc.)      Finally,  in  these    same  stages,  the  slates  of 
Stonesfield,  the  first  traces  of  Mammals  are  found,  namely 
the  jaws  and  teeth  of  animals  having  some  resemblance  to 
the  Opossum. 

486.  The  department  of  Mollusks  is  largely  represented 
in  all  its  classes.     The  peculiar  forms  of  the  primary  age 
have  almost  all  disappeared,  and  are  replaced  by  a  much 
greater  variety  of  new  forms.     Of  the  Brachiopods  only  one 

a  b  c  d 


Fig.  161. 

type  is  very  abundant,  namely,  the  Terebratula,  (Fig.  161,  a.) 
Among  the  other  Bivalves  there  are  many  peculiar  forms,  as 
the  Goniomya  (b)  and  the  Trigonia,  (c.)  The  Gasteropods 
display  a  great  variety  of  species,  and  also  the  Cephalopods, 
among  which  the  Ammonites  are  the  most  prominent,  (d.) 
There  are  also  found,  for  the  first  time,  numerous  represen- 
tatives of  the  Cutth-fishes,  under  the  form  of  Belemnites^ 


AGES    OF    NATURE. 


231 


(Fig.  162  )  an  extinct  type  of  animals,  protected  by  a  sheath, 
and  terminating  in  a  conical  body,  somewhat  similar  to  the 
bone  of  the  Sepia,  which        a 
commonly  is  the   only 
part  preserved,  (b.) 
487.    The  variety  is 

not     less      remarkable 

Fig.  162.  b 

among    the     Kadiates. 

There  are  to  be  found  representatives  of  all  the  classes  , 
even  traces  of  Jelly-fishes  have  been  made  out  in  the 
slate  of  Solenhofen,  in  Bavaria.  The  Polyps  were  very 
abundant  at  that  epoch,  aspecially  in  the  upper  stages,  one 
of  which  has  received  the  name  of  Coral-rag.  Indeed, 
there  are  found  whole  reefs  of  corals  in  their  natural  po- 
sition, similar  to  those  which  are  seen  in  the  islands  of  the 


Pacific.  Among  the  most  remarkable  types  of  stony  Polyps 
may  be  named  the  fan-like  Lobophyllia,  (L.flabellum,  a,) 
and  various  forms  of  tree-corals,  Lithodendron  pseudosty- 
tina,  b.)  But  the  greatest  variety  exists  among  the  Echino- 
derms.  The  Crinoids  are  not  quite  so  numerous  as  in 
former  ages.  Among  the  most  abundant  are  the  Pentacri- 
7iM5,  (c.)  There  are  also  Comatula-like  animals,  that  is  to 
say,  free  Crinoids  (Pterocoma  pinnata,  d.)  Many  Star- 
fishes are  likewise  observed  in  the  various  stages  of  this 
formation.  Finally,  there  is  an  extraordinary  variety  of 


232 


GEOLOGICAL    SUCCESSION    OF   ANIMALS 


Echini,  among  them  Cidaris,  (e,)  with  large  spines,  and 
several  other  types  not  found  before,  as,  for  example  the 
Dysaster,  (f)  and  the  NucleoUtes,  (g.) 

488.  The  fauna  of  the  Cretaceous  period  bears  the 
same  general  characters  as  the  Oolitic,  but  with  a  more 
marked  tendency  towards  existing  forms.  Thus,  the  Ich- 
thyosauri and  Plesiosauri,  that  characterize  the  preceding 
epoch,  are  succeeded  by  gigantic  Lizards,  more  nearly 
approaching  the  Reptiles  of  the  present  day.  Among  the 
Mollusks,  a  great  number  of  new  forms  appear,  especial- 
ly among  the  Cephalopods,*  some  of  which  resemble  the 


Fig.  164. 


Gasteropods   in   their    shape,  but   are    nevertheless   cham- 
bered.    The  Ammonites  themselves  are  quite  as  numerous 


Fig.  165 


as  in  the  Oolitic  period,  and  are  in  general  much  orna- 
mented, («.)  The  Acephala  furnish  us,  also,  with  peculiai 
types,  not  occurring  elsewhere,  Magas,  (a,)  the  Inoceramus 


*  («0  Ammonites;    (b)    Crioceras ;    (c)    Scaphites ;     (d)  Ancyloceras 
(e)  Hamites-  (/)   Baculites;  (g]  Turrilites. 


AGES    OF    NATURE.  233 

(5,)  the  Hippurites,  (c,)  and  peculiar  Spondyli,  with  long 
spines,  (d.)  There  is  also  a  great  variety  of  Gastro- 
pods, among  which  are  some  peculiar  forms  of  Plcu 


Fig.  166. 

Totomaria,  (e.)     The  Radiates  are  not  inferior  to  the  others 
in  variety.* 

489.  TERTIARY  AGE.  Reign  of  Mammals.  —  The  most 
significant  characteristic  of  the  Tertiary  faunas  is  their 
great  resemblance  to  those  of  the  present  epoch.  The  am 
mals  belong  in  general  to  the  same  families,  and  mostly 
to  the  same  genera,  differing  only  as  to  the  species.  And 
the  specific  differences  are  sometimes  so  slightly  marked, 
that  a  considerable  familiarity  with  the  subject  is  required, 
in  order  readily  to  detect  them.  Many  of  the  most  abundant 
types  of  former  epochs  have  now  disappeared.  The  changes 
are  especially  striking  among  the  Mollusks,  the  two  great 
families  of  Ammonites  and  Belemnites,  which  present  such 
an  astonishing  variety  in  the  Oolitic  and  Cretaceous  epochs, 
being  now  completely  wanting.  Changes  of  no  less  impor- 
tance take  place  among  the  Fishes,  which  are  for  the  most 
part  covered  with  horny  scales,  like  those  of  the  present 
epoch,  while  in  earlier  ages  they  were  generally  covered 
with  enamel.  Among  the  Radiata,  we  see  the  family  of 
Crinoids  reduced  to  a  very  few  species,  while,  on  the  other 
hand,  a  great  number  of  new  Star-fishes  and  Sea-urchins 
make  their  appearance.  There  are,  besides,  innumerable 

*  (a)  Diploctenium  cordatum ;  (b)  Marsupites ;  (c)  Salenia ;  (d)  Ga 
leritet  ,*  \?)  Micrayfer  cor-arquinum. 
20* 


234 


GEOLOGICAL    SUCCESSION    OF    ANIMALS. 


Fig.  167. 


remains  of  a  very  peculiar  type  of  animals,  almost 
unknown  to  the  former  ages,  as  well  as  to 
the  present  period.  They  are  little  cham- 
bered shells,  known  to  geologists  under  the 
name  of  Nummulites,  from  their  coin-like  ap- 
pearance, and  form  very  extensive  layers  of 
rocks,  (Fig.  167.) 

490.  But  what  is  more  important  in  a  philosophical  point 
of  view  is,  that  aquatic  animals  are  no  longer  predominant 
in  Creation.     The  great  marine  or  amphibian  reptiles  give 
place  to  numerous  mammals  of  great  size ;  for  which  rea- 
son, we  have  called  this  age  the  Reign  of  Mammals.     Here 
are    also   found    the    first   distinct   remains    of  fresh-water 
animals. 

491.  The   lower  stage   of  this  formation  is  particularly 
characterized  by  great  Pachyderms,  among  which  we  may 
mention  the  Paleotherium   and  Anoplotherium,  which  have 
acquired    such   celebrity   from    the    researches   of    Cuvier. 
These  animals,  among  others,  abound  in  the  Tertiary  forma- 
tions of  the  neighborhood  of  Paris.     The  Paleotheriums,  of 


Fig.  168.  Fig.  169. 

which  several  species  are  known,  are  the  most  common ; 
they  resemble,  (Fig.  168,)  in  some  respects,  the  Tapirs, 
while  the  Anoplotheriums  are  more  slender  animals,  (Fig. 
169.)  On  this  continent  are  found  the  remains  of  a  most 
extraordinary  animal  of  gigantic  size,  the  Basilosaurus,  a 
true  cetacean.  Finally,  in  these  stages,  the  earliest  remains 
of  Monkeys  have  boon  detected. 


AGES    OF    NATURE.  235 

492.  The  fauna  of  the  upper  stage  of  the  Tertiary  forma- 
tion approaches  yet  more  nearly  to  that  of  the  present  epoch. 
Besides  the  Pachyderms,  that  were  also  predominant  in  the 
lower  stage,  we  find  numbers  of  carnivorous  aiimals,  some 
of  them  much  surpassing  in  size  the  lions  and  tigers  of  our 
day.     We  meet  also  gigantic  Edentata,  and  Rodents  of  great 
size. 

493.  The  distribution  of  the  Tertiary  fossils  also  revoals 
to  us  the  important  fact,  that,  in  this  epoch,  animals  of  the 
same  species  were  circumscribed  in  much  narrower  limits 
than    before.     The    earth's   surface,   highly   diversified    by 
mountains  and  valleys,  was  divided  into  numerous   ba  'ns, 
which,  like  the  Gulf  of  Mexico,  or  the  Mediterranean  of  this 
day,  contained  species  not  found  elsewhere.     Such  was  the 
basin  of  Paris,  that  of  London,  and,  on  this  continent,  that  of 
South  Carolina. 

494.  In  this   limitation    of  certain   types   within   certain 
bounds,  we  distinctly  observe  another  approach  to  the  present 
condition  of  things,  in  the  fact  that  groups  of  animals  which 
occur  only  in  particular  regions  are  found  to  have  already 
existed  in  the  same  regions  during  the  Tertiary  epoch.     Thus 
the  Edentata  are  the  predominant  animals  in  the  fossil  fauna 
of  Brazil  as  well  as  in  its  present  fauna ;  and  Marsupials  were 
formerly  as  numerous   in  New  Holland  as  they  now  are, 
though  in  general  of  much  larger  size. 

495.  THE  MODERN  EPOCH.    Reign  of  Man. — ThePreseii* 
epoch  succeeds  to,  but  is  not  a  continuation  of,  the  Tertiary 
age.     These  two  epochs  are  separated  by  a  great  geological 
event,  traces  of  which  we  see  every  where  around  us      The 
climate  of  the  northern  hemisphere,  which  had  been,  during 
the  Tertiary  epoch,  considerably  warmer  than  now,  so  as  to 
allow  of  the  growth  of  palm-trees  in  the  temperate  zone  of 
our  time,  became  much  colder  at  the  end  of  this  period, 
causing  the  polar  glaciers  to  advance  south,  much  beyond 


236  GEOLOGICAL    SUCCESSION    OF   ANIMALS. 

their  previous  limits.  It  was  this  ice,  either  floating  like  ice- 
bergs, or,  as  there  is  still  more  reason  to  believe  noving 
along  the  ground,  like  the  glaciers  of  the  present  day,  that,  in 
its  movement  towards  the  South,  rounded  and  polished  the 
hardest  rocks,  and  deposited  the  numerous  detached  frag- 
ments brought  from  distant  localities,  which  we  find  every 
where  scattered  about  upon  the  soil,  and  which  are  known 
under  the  name  of  erratics,  boulders,  or  grayheads.  This 
phase  of  the  earth's  history  has  been  called,  by  geologists, 
the  Glacial  or  Drift  period. 

496.  After  the  ice  that  carried  the  erratics  had   melted 
away,  the  surface  of  North  America  and  the  North  of  Europe 
was  cov-ered  by  the  sea,  in  consequence  of  the  general  sub- 
sidence of  the  continents.     It   is  not  until  this  period  thai 
we  find,  in  the  deposits  known  as  the  diluvial  or  pleistocene 
formation,  incontestable  traces  of  the  species  of  animals  now 
living. 

497.  It  seems,  from  the  latest  researches  of  Geologists, 
that  the  animals  belonging  to  this  period   are  exclusively 
marine ;  for,  as  the  northern  part  of  both  continents  was 
covered  to  a  great  depth  with  water,  and  only  the  summits 
of  the  mountains  were  elevated  above   it,  as  islands,  there 
was  no  place  in^  our  latitudes  where  land  or  fresh-water 
animals  could  exist.     They  appeared  therefore  at  a  later 
period,  after  the  water  had  again  retreated  ;  and  as,  from 
the  nature  of  their  organization,  it  is  impossible  that   they 
should  have  migrated  from  other  countries,  we  must  conclude 
that  they  were  created  at  a  more  recent   period  than  our 
marine  animals. 

498.  Among  these  land  animals  which  then  made  their 
appearance,  there  were  representatives  of  all  the  genera 
and  species  now  living  around  us,  and  besides  these,  many 
types  now  extinct,  some  of  them  of  a  gigantic  size,  such  as 
the  Mastodon ,  the  remains  of  which  ore  found  in  the  upper- 


CONCLUSIONS.  237 

most  strata  of  the  earth's  surface,  and  probably  the  very 
last  large  animal  which  became  extinct  before  the  creation 
of  man.* 


Fig.  170. 

499.  It  is  necessary,  therefore,  to  distinguish  two  periods 
in  the  history  of  the  animals  now  living ;  one  in  which  the 
marine  animals  were  created,  and  a  second,  during  which 
the  land  and  fresh- water  animals  made  their  appeart  nee,  and 
at  their  head  MAN.! 


CONCLUSIONS. 

500.  From  the  above  sketch  it  is  evident  that  there  is  a 
manifest  progress  in  the  succession  of  beings  on  the  surface 

*  The  above  diagram  is  a  likeness  of  the  splendid  specimen  disinterred 
at  Newburg,  N.  Y.,  now  in  the  possession  of  Dr.  J.  C.  Warren,  in  Boston  $ 
the  most  complete  skeleton  which  has  ever  been  discovered.  It  stands 
nearly  twelve  feet  in  height,  the  tusks  are  fourteen  feet  in  length,  and 
nearly  every  bone  is  present,  in  a  state  of  preservation  truly  wonderful. 

f  The  former  of  these  phases  is  indicated  in  the  frontispiece,  by  a  nar- 
row circle,  inserted  between  the  upper  stage  of  the  Tertiary  formation 
and  the  Reign  of  Ma-'  properly  so  called. 


238  GEOLOGICAL    SUCCESSION    OF   ANIMALS. 

of  the  earth.  This  progress  consists  in  an  increasing  simu 
larity  to  the  living  fauna,  and  among  the  Vertebrates,  espe 
cially,  in  their  increasing  resemblance  to  Man. 

501.  But  this   connection   is  not  the  consequence   of  a 
direct  lineage  between  the  faunas  of  different  ages.     There 
is   nothing   like    parental  descent   connecting   them.      The 
Fishes  of  the  Paleozoic  age  are  in  no  respect  the  ancestors 
of  the  Reptiles  of  the  Secondary  age,  nor  does  Man  descend 
from   the    Mammals   which  preceded   him   in  the  Tertiary 
age.     The  link  by  which  they  are  connected  is  of  a  higher 
and  immaterial  nature  ;  and  their  connection  is  to  be  sought 
in  the  view  of  the  Creator  himself,  whose  aim,  in  forming 
the  earth,  in  allowing  it  to  undergo  the  successive  changes 
which  Geology  has  pointed  out,  and  in  creating  successively 
all  the  different  types  of  animals  which  have  passed  away, 
was   to    introduce    Man    upon    the   surface   of    our   globe. 
Man    is   the    end   towards    which   all    the   animal   creation 
has  tended,  from  the  first  appearance  of  the  first  Palaeozoic 
Fishes. 

502.  In  the  beginning  His  plan  was  formed,  and  from  it 
He  has  never  swerved  in  any  particular.     The  same  Being 
who,  in  view  of  man's  moral  wants,  provided  and  declared, 
thousands  of  years  in  advance,  that  "  the  seed  of  the  woman 
shall  bruise  the  serpent's  head,"  laid  up  also  for  him  in  the 
bowels  of  the  earth  those  vast  stores  of  granite,  marble,  coal, 
salt,  and  the  various  metals,  the  products  of  its  several  revo- 
lutions ;  and  thus  was  an  inexhaustible  provision  made  for 
his  necessities,  and  for  the  development  of  his  genius,  age 
in  anticipation  of  his  appearance. 

503.  To  study,  in  this  view,  the  succession  of  animals  in 
time,  and  their  distribution  in  space,  is,  therefore,  to  become 
acquainted  with  the  ideas  of  God  himself.     Now,  if  the  suc- 
cession of  created  beings  on  the  surface  of  the  globe  is  the 
realization  of  an  infinitelj    wise  plan,  it  follows  that  there 


CONCLL  SIGNS.  239 

must  be  a  necessary  relation  between  the  races  of  ani 
mals  and  the  epoch  at  which  they  appear.  It  is  necessary, 
therefore,  in  order  to  comprehend  Creation,  that  we  com- 
bine the  study  of  extinct  species  with  that  of  those  now 
living,  since  one  is  the  natural  complement  of  the  other.  A 
system  of  Zoology  will  consequently  be  true,  in  proportion 
as  it  corresponds  with  the  order  of  succession  among  ani- 
mals. 


INDEX    AND    GLOSSARY. 


Abd6men,  the  lower  cavity  of  the 
body,  41. 

Abranchiates,  without  gills,  21. 

Acalepha,  a  class  of  Radiates,  many 
species  of  which  produce  tingling 
of  the  skin  when  handled,  23. 

Acephala,  mollusks  having  no  dis- 
tinct head,  like  clams,  22. 

Acoustic,  pertaining  to  the  sense  of 
hearing,  56. 

Actinia,  digestive  apparatus  of,  97. 

Actinoids,  23. 

Affinity,  relationship,  30,  87. 

Ages  of  Nature,  221. 

Albumen,  the  white  of  egg,  42,  111, 
138. 

Alimentary  canal,  97. 

Alimentation,  the  process  of  nutri- 
tion, 42. 

Allantois,  Allantoidian,  149. 

Alligator,  teeth  of,  105. 

Alternate  reproduction,  159 ;  con- 
sequences of,  167 ;  difference  be- 
tween, and  metamorphosis,  167. 

Ambling,  91. 

Amblyopsis  spelseus,  55. 

Ammonites,  22,  230,  232,  233. 

Amnios,  150. 

Amphibia,  95. 

Amphipods,  a  family  of  crusta- 
ceans. 

Amphioxus.  its  place  181. 

Amphiuma,  209. 

Analogy,  30. 

Ana  Ufa,  metamorphoses  of,  177. 

Ancyl6ceras,  232. 

Animalcule,  a  minute  animal,  24. 

Animal  heat,  122. 

Animal  life,  44 ;  organs  of,  44. 

Animals,  number  of,  27 ;  distribu- 
tion in  space,  186 ;  in  time,  214. 
21 


Animals  and  plants,  difference*  be» 

tween,  41. 
Animate,  possessed  of  animal  life, 

43. 

Anoplotherium,  234. 
Antenna,  the  jointed  feelers  ol  lob- 
sters, insects,  &c.,  77. 
Aorta,  the  great  bloodvessel  arising 

from  the  heart,  116. 
Aphides,  reproduction  of,  162,  163. 
Apophysis,  a  projection  from  the 

body  of  a  bone,  181. 
Apparatus  of  motion,  73. 
Aptera,  wingless  insects,  21. 
Aquatic,  living  in  water. 
Aqueous,  like  water. 
Aqueous  humor,  50. 
Arctic  fauna,  197. 
Areolar  tissue,  38. 
Arges,  225. 

Aristotle's  lantern,  102. 
Arm,  82 ;  different  forms  of,  83. 
Artery,  113. 
Articulates,  composed  of  joints,  like 

the    lobster    or    caterpillar,  21; 

number  of,  27. 
Ascidia,    bottle-shaped     mollusks 

without  a  shell. 
Assimilation,  the  change  of  blood 

into  bone,  muscle,  &c.,  122. 
Astacus  pellucidus,  55. 
Asteridae,  the  family  of  star-fishes, 

23. 
Auditory,  pertaining   to  the  sense 

of  hearing,  56. 
Auricle,  a  cavity  of  the  heart,  like 

a  little  ear,  115. 
Avicula  decussata,  224. 
Axolotl,  209. 

Baculites,  232. 


242 


INDEX    ^ND    GLOSSARY. 


Balanus,  the  barnacle,  176. 
Basilosaurus,  234. 
Batrachians,  the  frog  tribe,  20. 
Beak,  104. 

Belemnites,  230,  233. 
Bird-tracks,  in  red  sandstone,  229. 
Birds,  number  of,  27. 
Bivalve,  having  two  shells,  like  the 

clam,  27- 
Blastoderm,  the  embryonic   germ, 

141. 

Blind-fishes,  55. 
Blood,  111,  121. 
Boulders,  236. 
Brachionus,  jaws  of,  103. 
Brachiopods,  a   class  of  mollusks, 

22. 

Brain,  45. 

Branchiae,  gills,  120. 
Branchifers,      univalve      mollusks 

breathing  by  gills,  22. 
Bronchi,  tubes  branching  from  the 

windpipe  in  the  lungs,  119. 
Brontes,  225. 
Bryozoa,  23,  225. 
Bucania  expansa,  224. 

Calcareous,  composed  of  lime,  75, 

Campanularia,  reproduction  of,  165, 

170. 

Canine  teeth,  106. 
Caninia  flexuosa,  224. 
Canker-worm,  metamorphoses    of, 

176. 

Cannon-bone,  86. 
Canter,  91. 

Capillary  vessels,  113. 
Carapace,  the  upper  covering  of  the 

crab  or  tortoise,  75. 
Carbon,  the  basis  of  charcoal  and 

most  combustibles,  41. 
Carboniferous  rocks,  218,  228. 
Cariocrinus  ornatus,  224. 
Carnivora,  animals  feeding  on  flesh, 

20;  teeth  of,  107. 
Carpus,  the  wrist,  83. 
Cartilage,  gristle,  39. 
Cartilaginous  tissue,  38. 
Cell,  37 ;  nucleated,  38. 
Cellule,  a  little  cell,  37. 
Cephalopods,  mollusks  with  arms 

surrounding  the   head,  like  the 

cuttle-fish,  22. 

Cercaria,  reproduction  of,  160,  171. 
Cerebral,  pertaining  to  the  brain,  45. 
Cestracion  Philippi,  204. 


Cetaceans,  marine  animals  whiefc 
nurse  their  young,  like  the  whale, 
porpoise,  &c.,  20. 

Chaetetes  lycoperdon,  224. 

Chalaza,  the  albuminous  thread  by 
which  the  yolk  of  the  egg  is  sus- 
pended, 138. 

Chalk  formation.  £1 3. 

Chambers  of  the  eye,  60. 

Chamois,  192. 

Cheirotherium,  229. 

Chelonians,  reptiles  of  the  tortoiftj 
tribe,  20. 

Chorion,  151. 

Choroid,  coat  of  the  eye,  49. 

Chrysalis,  the  insect  in  its  passage 
from  the  worm  to  the  fly  state. 
174. 

Chyle,  100,  112. 

Chyme,  100,  112. 

Cicatricula,  141. 

Cilia,  microscopic  hairs,  like  eye 
lashes,  81,  112,  116,  120. 

Circulation,  97  ;  great,  111 ;  pulmo- 
nary or  lesser,  116;  complete, 
116;  incomplete,  116. 

Cirrhipedes,  Crustacea  having  curled 
feelers,  like  the  barnacles,  27. 

Class,  18. 

Clavicle,  the  collar-bone,  83. 

Climate,  influence  on  a  fauna,  188. 

Climbing,  92. 

Coccbsteus,  22b. 

Cochlea.  58. 

Cold-blooded  animals,  122. 

Coleopterous,  insects  with  hard 
wing  cases,  like  the  dor-bug,  27. 

Collar-bone,  83. 

Columnaria  alveolata,  224. 

Comatula,  metamorphosis  of,  179 
180. 

Condor,  191. 

Constancy  of  species,  67. 

Coral-rag,  231. 

Cornea,  the  transparent  portion  of 
the  eye,  49. 

Corpuscles,  minute  bodies,  39. 

Cossus  ligniperda,  muscles  of,  77- 

Cretaceous,  or  chalk  formation,  218 

Cricoid,  ring-like,  65. 

Crinoid,  lily-like  star-fishes,  23 

Cri6ceras,  232. 

Crustacea,  articulated  animals  hav- 
ing a  crust-like  covering,  like  the 
crab  and  horse-shoe,  27 :  heart 
of,  117. 

Crystalline  lens,  49. 


INDEX    AND   GLOSSARY. 


243 


O.enoids,    fishes    which    ht.ve    the 

edge  of  the  scales  toothed,  20. 
Cteuophori,  soft,  radiated  animals, 

moving  by  cilia,  23. 
Cutis,  128. 
Cuttle-fish,  jaws  of,  102;  heart  of, 

117;      metamorphosis     of,    180; 

mode  of  swimming,  95. 
Cyathocrinus  ornatissimus,  224. 
Cyathophyllum       quadrigemiuum, 

224. 
Cycloids,  fishes  with  smooth  scales, 

Deciduous,  not  permanent  during  a 

lifetime,  199. 
Deglutition,  the  act  of  swallowing, 

108. 
Dentition,  form  and  arrangement 

of  the  teeth. 
Department,  a  primary  division  of 

the  animal  kingdom,  18. 
Development     of    the    white-fish, 

145. 

Devonian  rocks,  218. 
Diaphragm,  the  partition  between 

the  chest  and  abdomen,  74,  119. 
Diastole,  the  dilatation  of  the  heart, 

115. 

Digestion,  97. 

Diploctenium  cordatum,  233. 
Dipterus,  226. 
Discophori,    disk-shaped    animals, 

like  the  jelly-fish,  23. 
Disk,  a  more  or  less  circular,  flat- 
tened body,  14. 
Distoma,  reproduction  of,  161  ;  in 

the  eye  of  the  perch,  171. 
Distribution    of    animals,  laws  of, 

186  ;  in  space,  186 ;  in  time,  214. 
Dodo,  its  disappearance,  210. 
Dorsal  cord,  143. 
Dorsal  vessel,  114. 
Dorsibranchiates,  mollusks  having 

gills  upon  the  back,  21. 
Drift,  219,  236. 
Drinking,  109. 

Duck-barnacle.    See  Anatifa. 
Dysaster,  232. 

Ear,  55. 

Echinoderms,  radiate  animals  arm- 
ed with  spines  externally,  like 
the  sea-urchin,  23. 

Fchmus,  the  sea-urchin,  23;  jaws 
of,  102 ;  heart  of  U7 ;  mode  of 
progres%ion,  81. 


Echinus  sangumolentus,  metamor- 
phosis of,  178. 

Egg,  131 ;  form  of,  133  ;  formation 
of,  133 ;  ovarian,  133 ;  laying  of, 
135 ;  composition  of,  137 ;  devel- 
opment of,  139  ;  of  Infusoria,  172. 

Elementary  structure  of  organized 
bodies,  36. 

Embryo,  the  young  animal  before 
birth,  33,  132 ;  development  of, 
139. 

Embryology,  131,  139;  importance 
of,  153. 

Endosmose,  127.     See  Exosmose. 

Engeena,  a  large  orang,  206. 

Entomostraca,  21. 

Eocene  formation,  218. 

Ephyra,  164,  169. 

Epidermis,  the  scarf-skin,  129. 

Epithelium-cells,  126. 

Equivocal  reproduction,  158. 

Erratics,  rolling  stones,  236. 

Euomphalus  hemisphericus,  224. 

Eurypterus  remipes,  225. 

Eustachian  tube,  57. 

Excretions,  127. 

Exhalation,  128. 

Exosmose  and  Endosmose,  the  pro- 
cess by  which  two  fluids  pass 
each  way  through  a  membrane 
which  separates  them,  so  as  to 
become  mingled,  127. 

Eye,  48 ;  simple,  51 ;  aggregate, 
53 ;  compound,  54 ;  destitution 
of,  55 ;  compared  to  a  camera 
obscura,  51. 

Fa9ette,  a  very  small  surface,  54. 
Family,  a  group  including  several 

genera,  18. 

Fauna,  186  ;  distribution  of,  194. 
Femur,  the  thigh  bme,  87. 
Fibula,   the  smallest  ol    the    two 

bones  of  the  leg,  87. 
Fins,  93. 
Fishes,  number  of,   27;   heart  of, 

116  ;  reign  of,  222,  223. 
Fissiparous  reproduction,  propaga 

tion  by  fissure  or  division,  156. 
Flight,  92. 

Flora,  influence  on  a  fauna,  187. 
Fluviatile,  pertaining  to  rivers,  27. 
Foraminifera,  22. 
Formation,  geological,  217. 
Fossil,  dug  from  the  earth,  applied 

to  the  remains  of  animals   and 

plants. 


244 


AND    GLOSSARY. 


Function,  the  office  which  an  organ 
is  designed  to  perform,  29. 

Galeopithecus,  its  facilities  for 
leaping,  93,  207. 

Galerltes,  233. 

Gallinaceous,  birds  allied  to  the  do- 
mestic fowl,  190. 

Gallop,  91. 

Ganglions,  scattered  nervous  mass- 
es, from  which  nervous  threads 
arise,  46. 

Ganoids,  fishes  having  large,  bony, 
enamelled  scales,mostly  fossil,  20. 

Gar-pike,  192. 

Gasteropods,  mollusks  which  crawl 
by  a  flattened  disk,  or  foot,  on 
the  under  part  of  the  body,  like 
the  snail,  22. 

Gastric  juice,  99. 

Gavial,  a  crocodile,  with  a  long, 
slender  head. 

Gemmiparous  reproduction,  propa- 
gation by  budding,  156. 

General  properties  of  organized 
bodies,  35. 

Genus,  17- 

Geographical  distribution  of  ani- 
mals, 186 ;  conclusions,  207. 

Geological  succession  of  animals, 
214 

Germ,  the  earliest  manifestation  of 
the  embryo,  42,  141. 

Germinative  disk,  133,  137,  141; 
vesicle,  133,  137, 138;  dot,137,138. 

Gestation,  the  carrying  of  the  young 
before  birth,  135. 

Gills,  31,  120,  124. 

Gizzard,  99. 

Glacial  period,  236. 

Glands,  127 ;  salivary,  127. 

Globules  of  chyle,  100. 

Glottis,  65. 

Goniomya,  230. 

Grallatores,  birds  with  long  legs  for 
wading,  20. 

Grand-nurses  of  Cercaria,  162. 

Granivorous,  birds  feeding  on  grain 

Grit,  coarse  sandstone,  216. 

Gullet,  99. 

Hamites,  232. 

Hand,  83. 

Harmony  of  organs.  106 

Harpes,225. 

Hearing,  53 

Heart,  114 


Herbivora,  animals  feeding  on  grass 
and  leaves,  20. 

Hibernation,  torpid  state  of  ani« 
mals  during  winter,  123. 

Hippurltes,  233. 

Holothurians,  soft  sea-slugs,  biche- 
le-mar,  23. 

Homogeneous,  uniform  in  kind, 126. 

Homology,  30. 

Humerus,  the  shoulder-bone,  81. 

Hyaline  matter,  pure,  like  glass,  39. 

Hydra,  egg  of,  133  ;  propagation  of, 
156,  158. 

Hydrogen,  a  gas  which  is  the  prin- 
cipal constituent  of  water,  41. 

Hydroids,  a  family  of  polyps,  23. 

Ichthyosaurus,  229,  232. 

Icterus  Baltimore,  nest  of,  70. 

Igneous,  that  have  been  acted  upon 
by  fire,  215. 

Iguanodon,  229. 

Imbibition,  127. 

Inanimate,  destitute  of  life,  43. 

Incisor  teeth,  106. 

Incubation,  hatching  of  eggs  by  the 
mother,  136. 

Infusoria,  microscopic  animals  in- 
habiting water,  not  yet  fully  ar- 
ranged in  their  proper  classes,  24, 
32 ;  motions  of,  40 ;  generation  of 
172. 

Inocoramus,  232. 

Inorganic,not  made  up  of  tissues,35. 

Insalivation,  108. 

Insects,  number  of,  27. 

Insessores,  perching  birds,  like 
birds  of  prey,  20. 

Instinct,  67,  69. 

Intelligence,  67,  68. 

Intercellular  passages,  37. 

Invertebrates,  animals  destitute  of 
a  back-bone. 

Iris,  the  colored  part  of  the  eye  40 

Is6telus,  225. 

Jelly-fish.     See  Medusa. 
Judgment,  68. 

Kidneys,  130. 

Labyrinthodon,  228. 

Lacertans,    animals  of  the  lizard 

tribe,  20. 
Lacteals,  vessels  which  take  up  the 

nutriment,  100 
Lamellibranchiates,  mollusks  hav 


INDEX    AND    GLOSSARY. 


245 


ing  gills  '.rranged.  in  sheets,  like 

the  clam  and  oyster,  22. 
Larva,  the  caterpillar  or  worm  state 

of  an  insect. 
Larynx,  65. 
Lasso-cells,  110. 
Layers  of  the  embryo,  142. 
Leaping,  91. 
Lemming,  190,  197. 
Leptaena  alternata,  224. 
Lestris,  72. 
Life,  35,  44. 
Limbs,  54. 

Limnea,  parasites  of,  160,  162 
Lingula  prima,  224. 
Lithodendron  pseudostylina,  231. 
Liver,  129. 

Lobophyllia  flabellum,  231. 
Lobsters,  mode   of  swimming,  94 ; 

nervous  system,  46. 
Locomotion,   79;    organs    of,   82; 

modes  of,  88. 
Loligo,  arms  of,  180. 
Lungs,  118. 
Lymphatic  vessels,  100. 

Magas,  232. 

Malacostraca,  21. 

Mammals,  animals  which  nurse 
their  young,  19  ;  number  of,  27 ; 
reign  of,  222,  233. 

Man,  reign  of,  222,  234 ;  races  of, 
212 ;  his  twofold  nature,  25. 

Manatee,  206. 

Manducata,  insects  furnished  with 
jaws,  21. 

Marchantia  polymorpha,  reproduc- 
tion of,  166. 

Marl,  earth  principally  composed 
of  decayed  shells  and  corals,  216. 

Marsupials,  animals  with  a  pouch 
for  carrying  their  young,  as  the 
opossum  ;  gestation  of,  183. 

Marsupkes,  233. 

Mastication,  101. 

Mastodon,  236. 

Matrix,  the  organ  in  which  the  em- 
bryo is  developed,  152. 

Medulla  oblongata,  continuation  of 
the  brain  into  the  back-bone. 

Medusa,  jelly-like  animals  living  in 
the  sea,  23 ;  development  of,  163 ; 
digestive  organs,  98  motion  80. 

Megalobatrachus,  209. 

Megalosaurus,  229. 

Melocrhius  amphbra,  224. 

Mem>ry,  68. 

21* 


Menobranchus,  202,  209. 

Menop6ma,  202,  209. 

Merganser,  an  aquatic  bird  allied  to 
the  goose,  66,  193. 

Metacarpus,  the  wrist,  83. 

Metatarsus,  87. 

Metamorphic  rocks,  216,  174. 

Metamorphosis,  149,  167;  of  the 
silk-worm,  175 ;  canker-worm, 
176:  duck-barnacle,  177;  star-fish, 
178;  comatula,  179. 

Micraster  cor-anguinum,  232. 

Miocene  formation,  219. 

Modern  age,  222,  235. 

Molar  teeth,  106. 

Molecules,  very  minute  particles,  35. 

Mollusks,  soft  animals  of  the  snail 
and  oyster  kind;  heart  of,  117; 
liver  of,  129 ;  number  of,  27 ;  meta- 
morphosis of,  179. 

Monkey,  teeth  of,  107,  205. 

Mon6culus,  mode  of  carrying  eggs, 
135  ;  motion,  73 :  apparatus  of,  73. 

Moulting,  the  shedding  of  feathers, 
hair,  &c.,  128. 

Muscles,  73;  disposition  of,  in  in- 
sects, 77 ;  in,  fishes,  78 ;  in  birds, 
79. 

Muscular  tissue,  39. 

Myxine  glutinosa,  its  eye,  55. 

Natatores,  birds  with  webbed  feet 
for  swimming,  20. 

Natica,  tongue  of,  102 ;  heart  of,  117. 

Nautili,  22. 

Neptunian  rocks,  215. 

Nereis,  jaws  of,  102 ;  gills  of,  81 ; 
eye,  53. 

Nervous  system,  44 ;  in  mammals, 
45 ;  in  articulates,  46 ;  in  crusta- 
ceans, 46  ;  in  radiates,  47. 

Nervous  tissue,  39. 

Nest  of  Baltimore  oriole,  70 ;  of  tai- 
lor bird,  70  ;  of  Ploceus,  71. 

Nomenclature,  the  naming  of  ob- 
jects and  their  classes,  family,  &c. 

Nostrils,  60. 

Notosaurus,  228. 

Nucleolites,  232. 

Nucleolus,  a  little  nucleus,  38. 

Nucleus,  a  kernel,  or  condensed 
central  portion,  38. 

Nudibranchiates,  mollusks  having 
the  gills  floating  externally,  fig.  91 

Nummulites,  234. 

Nurses,  of  Cercaria,  162;  of  ants 
and  bees,  163. 


246 


INDEX    AND    GLOSSARY. 


Nutrition,  96. 

Ocelli,  minute  eyes,  52. 

Octopus,  arms  of,  180. 

Odors,  61. 

(Esophagus,  the  gullet,  46,  99. 

Olfactory,  pertaining  to   the  sense 

of  smell,  45,  60. 
Omnivora,  feeding  upon  all  kinds 

of  food,  107. 
Oolitic  formation,  218. 
Operculum,  a  cover  for  the  aperture 

of  a  shell. 
Ophidians,  animals  of  the  serpent 

kind,  20. 
Optic  nerves,  48. 
Orbits,  48. 
Orders,  18. 
Organism,  37. 
Organized  bodies,  general  properties 

of,  35 :  elementary  structure,  36, 

37. 

Ornithichnites,  229. 
Orth6ceras  fusiforme,  225. 
Osseous  tissue,  39. 
Otolites,  little  bones  in  the  ears  of 

mollusks  and  Crustacea,  59. 
Ovary,   the   organ  in  which   eggs 

originate,  133. 
Oviduct,  the  passage  through  which 

the  egg  is  excluded,  134. 
Oviparous,  producing  eggs,  131. 
Ovis  montana,  192. 
Ovo-viviparous,       animals      which 

hatch    their    eggs    within    their 

body,  135. 
Ovul/ition,  the  production  of  eggs, 

134. 

Oxygen,  its  consumption  in  respira- 
tion, 41,  113,  121. 

Pachydermata,  thick-skinned  ani- 
mals, like  the  elephant,  hog,  &c., 
107,  234. 

Pacing,  91. 

Paleont61ogy,  215. 

Palaeozoic  age,  222,  223. 

Paleotherium,  234. 

Palpation,  the  exercise  of  the  touch, 

Palpi,  jointed  organs  for  touch, 
about  the  mouth  of  insects,  64. 

Papilla,  a  little  pimple,  62. 

Paramecia,  reproduction  of,  157. 

Parasitic,  living  on  other  objects. 

Passerine  birds  of  the  sparrow  kind 
201. 


Peduncle  cr  Pedicle,  a  slender  stem. 

Pelvis,  the  cavity  formed  by  the 
hip  bones,  87. 

Pentacrinus,  231 ;  metamorphosis 
of,  180. 

Perception,  67. 

Perchers,  a  class  of  birds,  20. 

Peripherie,  exterior  surface,  152. 

Peristaltic  motion,  100. 

Petrifactions,  215. 

Phalanges,  83. 

Pigment,  a  coloring  substance,  40. 

Pituitary  membrane,  61. 

Placenta,  the  organ  by  which  the 
embryo  of  mammals'  is  attached 
to  the  mother,  152. 

Placoids,  fishes  with  a  rough  skin, 
like  the  shark  or  skate,  20. 

Planaria,  its  digestive  apparatus, 
98 ;  an  eye  of,  53. 

Plant-lice.     See  Aphides. 

Plants  compared  with  animals,  41. 

Platynotus,  225. 

Pleiocene  formation,  219. 

Plesiosaurus,  229,  232. 

Pleurotomaria,  233. 

Ploceus  Philippinus,  nest  of,  70. 

Plutonic  rocks,  215. 

Podurella,  mode  of  leaping,  92 ;  em- 
bryo of,  144 ;  egg  of,  133. 

Polyps,  a  small  animal  fixed  at  one 
end,  with  numerous  flexible  feel- 
ers at  the  other,  27,  53;  repro- 
duction of,  158. 

Prehension,  act  of  grasping,  109. 

Primary  age,  222. 

Primitive  stripe,  143. 

Progression,  88,  90. 

Proligerous,  the  part  of  the  egg 
bearing  the  embryo,  141. 

Pr6teus,  209. 

Protosaurus,  228. 

Protractile,  capable  of  being  ex- 
tended. 

Pterichthys,  226. 

Pter6coma  pinnata,  231. 

Pterodactylus,  230. 

Pteropods,  mollusks  with  wing-like 
expansions  for  swimming,  22. 

Pulmonary,  relating  to  the  lungs, 
116. 

Pulmonates,  mollusks  which 
respire  air,  22. 

Pupil,  40. 

Pyrula,  egg-cases  of,  135. 

Quadrumanous,  four-handed,  201 


INDEX    AND    GLOSSARY. 


247 


Quadruped,  animals  with  four  legs, 
40. 

Radiata,  animals  whose  organs  ra- 
diate from  a  centre,  23,  27. 

Radius,  one  of  the  bones  of  the 
arm,  83. 

Reign  of  fishes ;  of  man,  235  ;  of 
mammals,  233  ;  of  reptiles,  238. 

Relation,  functions  of,  44. 

Reproduction,  131 ;  peculiar  modes, 
156. 

Reptiles,  number  of.  27;  reign  of, 
222,  227. 

Respiration,  97,  118. 

Rete  mucosum,  129 ;  retina,  49. 

Retractile,  that  may  be  drawn 
back,  84. 

Rhizodonts,  20 ;  of  the  trias,  228. 

Rhizopods,  22. 

Rocks,  classification  of,  215;  defi- 
nition of,  215. 

Rodents,  quadrupeds  with  teeth  for 
gnawing,  107. 

Rotifers,  jaws  of,  103  ;  eggs  of,  172. 

Ruminants,  quadrupeds  which  chew 
the  cud,  107. 

Running,  91. 

Rytma  Stelleri,  210. 

Salenia,  233. 

Saliferous  formation,  218. 

Saliva,  108. 

Salivary  glands,  127. 

Salpa,  reproduction  of,  159  ;  motion 
of,  80. 

Scansores,  birds  adapted  for  climb- 
ing, 20. 

Scaphites,  232. 

Scapula,  82. 

Sclerotic,  the  principal  coat  of  the 
eye,  49. 

Scutella,  jaws  of,  101. 

Sea-anemone.     See  Actinia. 

Sea-urchin,  eye  of,  53 ;  digestive 
organs,  98;  heart,  117. 

Secondary  age,  222,  227. 

Secretions,  97,  126. 

Sedimentary  rocks,  215. 

Segment,  portion  of  a  circle  or 
sphere. 

Sensation,  general,  43,  47. 

Senses,  special,  48. 

Sepia,  231. 

Serous,  watery,  142. 

Shark,  egg  of,  133. 

Shoulder-blade,  82. 


Sight,  48. 

Silex,  flinty  rock. 

Siliceous,  made  of  mnt. 

Silk-worm,  metamorphosis  of,  176. 

Silurian  rocks,  lower,  217;  upper 
218. 

Sinuous,  bending  in  and  out,  22. 

Siphonophori,  23. 

Siren,  209. 

Skeleton,  74,  77. 

Skin,  structure  of,  128. 

Smell,  60. 

Species,  constancy  of.  67;  definition 
of,  17,  159. 

Spinal  marrow,  45. 

Spondyli,  233. 

Sponges  not  animal,  41. 

Spontaneous  generation,  171. 

Spores,  the  germs  of  sea-weeds 
ferns,  &c.,  170. 

Standing,  88. 

Stapes,  57. 

Star-fish,  metamorphoses  of,  178 
eye  of,  53 ;  mode  of  progression, 
81 ;  reproduction  of  parts,  126. 

Stigmata,  openings  in  insects  for 
the  admission  of  air,  118. 

Stomach,  97. 

Stratified  rocks,  215. 

Stratum,  a  layer. 

Strobila,  164,  169. 

Structure  of  the  earth's  crust,  214 

Sturgeon,  compared  with  white- 
fish,  180. 

Suctoria,  insects  taking  their  food 
by  suction,  21. 

Swimming,  93. 

Sylvia  sutoria,  nest  of,  70. 

Systole,  the  contraction  of  the  heart 
to  force  out  the  blood,  115. 

Tape-worm,  reproduction  of,  140. 

Tapir,  204,  234. 

Tarsus,  the  ancle,  87. 

Taste,  62. 

Teeth,  104. 

Temperate  faunas,  198. 

Temporal,  relating  to  the  temples, 

Tentacle,  the  horn-like  organs  on 
the  head  of  mollusks,  usually 
bearing  the  eyes,  52. 

Terebratula,  230. 

Tertiary  age,  222,  233. 

Tertiary  formation,  lower,  218 ;  up 
per,  219. 


248 


INDEX   AND    GLOSSARY. 


Test,  the  bristle  crust  covering  the 
crustaceans,  &c.,  75. 

Teuthidcans,  the  family  of  cuttle- 
fishes, 22. 

Tibia,  one  of  the  bones  of  the  leg,  87. 

Tissues,  37 ;  areolar,  38 ;  cartilagi- 
nous, 38  ;  muscular,  39  ;  osseous, 
39 ;  nervous,  39. 

Tongue,  62. 

Touch,  63. 

Trachea,  the  windpipe,  119. 

Tracheae,  the  air-tubes  of  insects, 
118,  123. 

Transudation,  127. 

Trias  formation,  218,  228. 

Trigonia,  230. 
rUobites,  21,  32. 

TrochoUtes  ammonius,  225. 

Trophi,  organs  for  feeding,  of  in- 
sects, crabs,  &c. 

Tropical  faunas,  204. 

Trot,  91. 

Tubulibranchiates,  21. 

Tunicata,  mollusks  with  a  leathery 
covering,  159. 

Turrilites,  232. 

Tympanum,  a  drum ;  the  membrane 
separating  the  internal  and  exter- 
nal ear,  57. 

Type,  an  ideal  image,  18. 

Ulna,  one  of  the  bones  of  the  arm, 

83. 

Ultimate,  final. 
Univalve,  having  a  single  shell,  like 

the  snail,  27. 

Vascular,  composed  of  vessels,  129 
Vegetative  life,  44,  96;  layer,  142. 
Veins,  lia 


Ventricle,  a  cavity  of  the  heart,  116 

Vermicular,  100. 

Vertebra,  a  joint  of  the  back -bone, 

46,  77. 
Vertebrate,  having  a  back-bone,  19, 

Vertical,  in  a  perpendicular  direc- 
tion, 48 

Vesicle,  a  small  membranous  bag, 
37. 

Vestibule,  a  porch  ;  the  entrance  to 
one  of  the  cavities  of  the  ear,  58. 

Vibratile,  moving  to  and  fro,  112. 

Viscera,  159. 

Vitelline  membrane,  138. 

Vitellus,  137. 

Vitreous  humor,  50. 

Viviparous,  producing  living  young, 
131. 

Vocal  cords,  65. 

Voice,  64. 

Voluntary,  under  control  of  the  will, 
43. 

Vorticella,  reproduction  of,  157, 158 

Walking,  90. 

Wapiti,  211. 

Warm-blooded  animals,  122. 

Water-tubes  of  aquatic  animals,  123. 

Whale,  fans  of,  104. 

Whales,  mode  of  swimming,  94. 

White-fish,  development  of,  145. 

Windpipe,  119. 

Worms,  21 ;  eye  of,  53. 

Zoology,  its  sphere,  25. 
Zoophytes,  animals  of  a  very  lo\V 

type,  mostly  fixed  to  the  ground. 

of  a  plant-like  form. 


249 


LIST  OF  THE  MOST  IMPORTANT  AUTHORS 

WHO    »  AY  BE   CONSULTED   IN    REFERENCE   TO   THE 
SUBJECTS   TREATED   IN   THIS  WORK 


GENERAL  ZOOLOGY. 

Aristotle's  Zoology;  Linnseus,  System  of  Nature;  Cuvier's  Animal 
Kingdom;  Oken's  Zoology;  Humboldt's  Cosncos,  and  Views  of  Nature; 
Spix,  History  of  Zoological  Systems ;  Cuvier's  History  of  the  Natural 
Sciences. 


ANATOMY  AND  PHYSIOLOGY. 

Henle's  General  Anatomy ;  and  most  of  the  larger  works  on  Compara- 
tive Anatomy,  Physiology,  and  Botany,  such  as  those  of  Hunter,  Cuvier, 
Meckel,  Mailer,  Todd  and  Bowman,  Grant,  Owen,  Carpenter,  Rymer 
Jones,  Hassall,  Quain  and  Sharpey,  Bourgery  and  Jacob,  "Wagner, 
Siebold,  Milne  Edwards,  Carus,  Schleiden,  Burmeister,  Lindley,  Robert 
Brown,  Dutrochet,  Decandolle,  A.  Gray. 


ON  SPECIAL  SUBJECTS  OP  ANATOMY  AND  PHYSIOLOGY  MAY  BB 
CONSULTED 

Schwann,  on  the  Conformity  in  the  Structure  and  Growth  of  Animals 
and  Plants. 

Dumas  and  Boussingault,  on  Respiration  in  Animals  and  Plants. 

Valentin,  on  Tissues  ;  and  Microscopic  Anatomy  of  the  Senses. 

Soemmering,  Figures  of  the  Eye  and  Ear. 

Kolliker,  Theory  of  the  Animal  Cell. 

Breschet,  on  the  Structure  of  the  Skin. 

Locomotion  ;  Weber,  and  Duges. 

Teeth;  Fred.  Cuvier,  Geoff.  St.  Hilaire,  Owen,  Nasmyth,  Retzius. 

Blood;  Dollinger,  Barry. 

Digestion;  Spallanzani,  Valentin  and  Brunner,  Dumas  and  Boussin 
gault,  Liebig,  Matteucci,  Beaumont. 


INSTINCT  AND  INTELLIGENCE. 
Kirby,  Blumenbach,  Spurzheim,  Combe. 


250 

EMBRYOLOGY. 

D' Alton,  Von   Baer,  Purkinje,  Wagner,  Wolfe,    Rathke,    Bischoff 
Velpeau,  Flourens,  Barry,  Leidy. 


PECULIAR  MODES  OF  REPRODUCTION. 
Ehrenbcrg,  Trembly,  ROsel,  Sars,  Loven,  Steenstrup,  Van  Beneden. 

METAMORPHOSIS. 

St.  Merian,  Rosel,  De  Geer,  Harris,  Kirby  and  Spence,  Bunneister 
Reaumur. 

GEOGRAPHICAL  DISTRIBUTION. 

Zimmerman,  Milne  Edwards,  Swainson,  A.  Wagner,  Forbes,  Pennant, 
Richardson,  Ritter,  Guyot. 

GEOLOGY. 

The  Works  of  Murchison,  Phillips,  Lyell,  Mantell,  Hugh  Miller, 
Agassiz,  D'Archiac,  De  Beaumont,  D'Orbigny,  De  Verneuil,  Cuvier, 
Brongniart,  Deshayes,  Morton,  Hall,  Conrad,  Hitchcock,  Troost,  and  the 
Reports  on  the  various  local  Geological  Surveys. 

Very  many  of  the  papers  of  the  authors  above  referred  to  are  not  pub- 
lished in  separate  volumes,  but  are  scattered  through  the  volumes  Oi 
Scientific  Periodicals  ;  such  as  the 

Transactions  of  the  Royal  Society  of  London. 

Annals  and  Magazine  of  Natural  History. 

Annales,  and  Archives,  du  Museum  d'  Hist.  Natuielie. 

Annales  des  Sciences  Naturelles. 

Wiegmann's  Archiv  fdr  Naturgeschichte. 

Mailer's  Archiv. 

Oken's  Isis. 

Berlin  Transactions. 

Transactions  of  the  American  Philosophical  Society 

Memoirs  of  the  American  Academy. 

Journal  of  the  Academy  of  Nat.  Sciences,  Philadelphia. 

Silliman's  Journal 

Journal  of  Boston  Society  of  Natural  History. 


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